Lantibiotic-based compounds having antimicrobial activity

ABSTRACT

The present invention provides actagardine, actagradine B and deoxy actagardine B derivatives of formula (I), 
     
       
         
         
             
             
         
       
     
     wherein: X1 denotes that the residue is Leu; Val; or Ile; X2 denotes that the residue is Leu; Val; or Ile; R 1  represents an alkyl or heteroalkyl group, substituted by at least one hydroxyl substituent, and R 2  represents hydrogen, or an alkyl or heteroalkyl group, optionally substituted by at least one hydroxyl substituent, or R 1  and R 2  taken together with the nitrogen atom represent a heterocyclic group having at least one hydroxyl substituent, wherein the heterocyclic group optionally further contains one or more heteroatoms; Z is an amino acid residue, —NR 3 R 4 , —NR 5 COR 6 , —NR 5 C(O)OR 6 ; —NR 5 SOR 6 , NR 5 SO 2 R 6 ; —NR 5 C(S)NR 6 R 7 , —NR 5 C(NR 8 )NR 6 R 7 , or —N═R 9 , where R 3 , R 4 , R 5 , R 6 , R 7 , R 8  and R 9  are independently hydrogen, or a group, optionally substituted, selected from alkyl, heteroalkyl, aryl, heteroaryl, aralkyl and heteroaralkyl, with the proviso that R 9  is not hydrogen; and Y is —S— or —S(O)—. The compounds find use in the treatment of microbial infections.

RELATED APPLICATION

This application is related to GB patent application 0714029.6 filed 18 Jul. 2007; the contents of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to lantibiotic-based compounds having antimicrobial activity, the methods for their production, and their use.

BACKGROUND

The lanthionine-containing antibiotic peptides, or “lantibiotics”, are a group of natural products secreted by various Gram-positive bacteria. The defining structural feature of this class of compounds is the presence of the thioether amino acids lanthionine and methyllanthionine, formed via specialised biosynthetic pathways acting on ribosomally synthesised, linear peptide precursors.

Lantibiotics have been classified into two classes, type-A and type-B. Type-A lantibiotics are generally elongate amphiphiles that retain substantial linear sections in their structure. Examples of type-A lantibiotics are nisin and subtilin. Nisin and related molecules can bind to lipid II, an indispensible intermediate in bacterial cell wall synthesis. In addition, the type-A lantibiotics are capable of forming pores in plasma membranes. The potent antimicrobial activity of the type-A lantibiotics is thought to derive from the combination of their lipid II binding and pore forming capabilities.

Type-B lantibiotics are generally smaller peptides that are folded and cross-linked into globular shapes and lack extensive linear peptide sections. Examples of type-B lantibiotics are Mersacidin, Actagardine and Cinnamycin. Like the type-A lantibiotics they have antimicrobial activity that is believed to derive mainly from their ability to bind to Lipid II, as they are not capable of forming pores in the bacterial membranes.

Mersacidin and actagardine have potent antibacterial activity against a range of Gram-positive organisms including Streptococcus, Enterococcus and Clostridium species.

For reviews, see Sahl and Bierbaum (1998) Annual Rev. Microbiol. 52:41-79; van Kraaij, de Vos, Siezen and Kuipers, Nat. Prod. Rep. 1999, 16, 575; Chatterjee, Paul, Xie and van der Donk, Chem. Rev. 2005, 105, 633.

Actagardine and analogues have been reported to be produced by two species of Actinoplanes; A.garbadinensis and A. liguriae [Parenti, Pagani, Beretta, J. Antibiotics, 1976, 29, 501; U.S. Pat. No. 6,022,851]. Actagardine is produced from a pre-pro-peptide, the C-terminal portion of which has the polypeptide sequence of SSGWVCTLTIECGTVICAC. This polypeptide is modified by the following crosslinks, creating secondary and tertiary structure: crosslink 1-6, Lanthionine (Ser-Cys); crosslink 7-12, Beta-methyllanthionine (Thr-Cys); crosslink 9-17, Beta-methyllanthionine (Thr-Cys); crosslink 14-19, Beta-methyllanthionine sulfoxide (Thr-Cys). Also co-produced is an analogue [Zimmerman, Metzger and Jung, Eur. J. Biochem 1995, 228, 786] in which the crosslink 14 and 19 is not oxidized i.e. it is a beta-methyllanthionine not betamethyllanthionine sulfoxide which is named herein deoxyactagardine.

A further variant, herein called deoxyactagardine B, derived from a propeptide with a C-terminal sequence SSGWVCTLTIECGTLVCAC and lacking a sulphoxide on the crosslink between residues 14 and 19 has also been isolated from A. liguriae (as discussed in co-pending application PCT/GB2007/000138 (WO/2007/083112), which is herein incorporated by reference).

The structures of actagardine and deoxyactagardine B are shown below.

U.S. Pat. No. 6,022,851 describes the isolation of actagardine and related forms from isolated strains of A. garbadinensis and A. liguriae.

DISCLOSURE OF THE INVENTION

The present invention relates to lantibiotic-based compounds having antimicrobial activity, the methods for their production, and their use. These compounds have a similar spectrum of anti-microbial activity to actagardine and provide new and useful alternatives to this lantibiotic. In one aspect, the present invention provides novel derivatives of actagardine, actagardine B and deoxyactagardine B. In another aspect, the lantibiotic-based compounds of the invention are prepared by modification of the C-terminus, and optionally the N-terminus, of lantibiotics, and lantibiotic variants and derivatives. The compounds of the invention may have improved antimicrobial activity in comparison to the actagardine, actagardine B and deoxyactagardine B compounds from which they are derived.

The invention also provides pharmaceutical compositions comprising a compound of the invention together with a pharmaceutically acceptable carrier or diluent.

In a further aspect, the present invention provides the use of the compounds and compositions of the invention in therapy. Particularly, the present invention provides methods for the treatment or prophylaxis of a microbial infection in a subject, the methods comprising administering to said subject a compound or composition of the invention. The compound or composition may be administered orally, rectally, intravenously, vaginally, intramuscularly or topically. Most preferably the compounds and compositions of the invention are administered orally. The infection may be a bacterial infection. Preferably, the infection is a Clostridium infection, preferably a Clostridium perfringens, Clostridium difficile, Clostridium tetani or Clostridium botulinum infection, most preferably C. difficile infection. These methods provide new and useful alternatives to methods of treatment utilising a type-A lantibiotic, vancomycin or metronidazole.

The compounds described herein, and derivatives and variants thereof, may be selective for C. difficile. These compounds may have reduced activity against other commensal gut flora, particularly Bifidobacterium spp and Bacteroides spp, compared to vancomycin or metronidazole.

The compounds described herein have similar activity against C. difficile as vancomycin and provide new and useful alternatives to vancomycin in a method of treatment or prophylaxis of a microbial infection in a subject.

The compounds described herein may have increased stability to enzymatic degradation compared to nisin. Particularly, the compounds may have improved stability to intestinal juices compared to nisin. The type-B lantibiotic structures, upon which the present compounds are based, are more compact than type-A compounds and they do not have the extensive linear character of the A-forms. Consequently, they are less vulnerable to proteolysis and are therefore more likely to reach the site of an infection, such as a bacterial infection of the lower intestinal tract.

The invention also provides the use of the compounds and compositions of the invention as antimicrobials for use in vivo or in vitro.

In a further aspect, the present invention provides methods for synthesising compounds of the invention from a lantiobiotic or variants and/or derivatives thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the efficacy in vivo of compound III in the hamster model of C. difficile-associated cecitis.

FIG. 2 shows the efficacy in vivo of compound I in the hamster model of C. difficile-associated cecitis.

FIG. 3 shows the course of the reaction forming compound I as followed by analytical HPLC. FIGS. 3 (a) to (c) show the conversion of deoxyactagardine B to the monoamide Compound I and a small amount of the diamide during the course of the reaction.

FIG. 4 shows the stability of (a) nisin and mersacidin and (b) compounds I and III in simulated gastric fluid (SGF).

FIG. 5 shows the stability of (a) nisin and mersacidin and (b) compound III in simulated intestinal fluid (SIF).

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to compounds based on lantibiotics, particularly type-B lantibiotics such as actagardine, actagradine B and deoxy-actagardine B.

The lantibiotic-based compounds provided herein may have improved solubility and/or other physicochemical properties and/or biological activity compared to the parent lantibiotics from which they are derived. Improved solubility has significant advantages for the purposes of formulation of the compounds of the invention for the purpose of oral and intravenous administration. Furthermore, improved solubility allows for higher concentrations of antibiotic to be present at the site of action, potentiating greater efficacy.

Compounds

In a first aspect of the present invention there is provided a compound of formula (I):

wherein A is a Leu; Val; or Ile amino acid side chain; B is a Leu; Val; or Ile amino acid side chain; X is —NR¹R²; and Y, Z, R¹ and R² are as defined below, or a pharmaceutically acceptable salt thereof.

Alternatively, the structure of the compound may be represented conveniently thus:

wherein:

X1 denotes that the residue is Leu; Val; or Ile;

X2 denotes that the residue is Leu; Val; or Ile;

R¹ represents an alkyl or heteroalkyl group, substituted by at least one hydroxyl substituent, and R² represents hydrogen, or an alkyl or heteroalkyl group, optionally substituted by at least one hydroxyl substituent, or Wand R² taken together with the nitrogen atom represent a heterocyclic group having at least one hydroxyl substituent, wherein the heterocyclic group optionally further contains one or more heteroatoms;

Z is an amino acid residue, —NR³R⁴, —NR⁵COR⁶, —NR⁵C(O)OR⁶; —NR⁵SOR⁶, —NR⁵SO₂R⁶; —NR⁵C(S)NR⁶R⁷, —NR⁵C(NR⁸)NR⁶R⁷, or —N═R⁹, where R³, R⁴, R⁵, R⁶, R⁷, R⁸ and R⁹ are independently hydrogen, or a group, optionally substituted, selected from alkyl, heteroalkyl, aryl, heteroaryl, aralkyl and heteroaralkyl, with the proviso that R⁹ is not hydrogen;

Y is —S— or —S(O)—;

or a pharmaceutically acceptable salt thereof. In a further aspect, the invention provides variants and biologically active derivatives of these compounds.

DEFINITIONS

It will be understood by reference to Z being a group —NH₂, that this moiety represents the N-terminus of the alanine residue at position 1 of the above compound. By reference to the group Z being an amino acid residue, it will be understood that this moiety represents an amino acid, conventionally referred to in the art as Xaa(0), linked to the alanine at position 1 via an amide bond. By reference to the group Z being —NR³R⁴, —NR⁵COR⁶, —NR⁵C(O)OR⁶; —NR⁵SOR⁶, —NR⁵SO₂R⁶; —NR⁵C(S)NR⁶R⁷, —NR⁵C(NR⁸)NR⁶R⁷, or —N═R⁹, it will be understood that these groups represent modifications of the N-terminus of the alanine at position 1.

In the representation above it will be appreciated that the amino acid residues are denoted by the appropriate three letter code. Abu refers to a 4-aminobutyric acid-derived amino acid residue, as will be clear from the structural formula.

It will also be understood by reference to the group —NR¹R² (—X), that this moiety represents a group linked to the alanine residue at position 19 via an amide bond, i.e. where the nitrogen atom to which R¹ and R² is attached forms part of the amide bond. It will be understood that this group represents a modification of the C-terminus of the alanine at position 19.

It will also be appreciated that a reference to Z being an amino acid residue is a reference to a group —NR⁶COR⁶ where R⁶ represents the amino- and side chain-functionality of an amino acid residue. For example, for the amino acid residue glycine, R⁶ is —CH²NH₂. Typically, for an amino acid residue, R⁶ is a C₁₋₇, alkyl group having an amino substituent and optionally further substituted as appropriate.

Where X1 and X2 are Val and Ile respectively, and Y is —S(O)—, the compound may be referred to as an actagardine derivative.

Where X1 and X2 are Leu and Val respectively, and Y is —S—, the compound may be referred to as a deoxy-actagardine B derivative.

Where X1 and X2 are Leu and Val respectively, and Y is —S—, Z is —NH₂, R¹ is —CH₂CH₂OH and R² is hydrogen, the compound is also referred to as deoxy-actagardine B N-[2-ethanolamine]monocarboxamide.

Alkyl: The term “alkyl” as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from a carbon atom of a hydrocarbon compound having from 1 to 20 carbon atoms (unless otherwise specified) and which may be saturated or unsaturated (e.g. partially unsaturated, fully unsaturated).

Heteroalkyl: The term “Heteroalkyl” as used herein refers to an alkyl group having one or more carbon atoms replaced with a N, S, or O heteroatom.

In the context of alkyl groups, the prefixes (e.g. C₁₋₄, C₁₋₇, C₁₋₂₀, C₂₋₇, C₃₋₇, etc.) denote the number of carbon atoms, or range of number of carbon atoms. For example, the term “C₁₋₄ alkyl”, as used herein, pertains to an alkyl group having from 1 to 4 carbon atoms. Examples of groups of alkyl groups include C₁₋₄ alkyl (“lower alkyl”), C₁₋₇ alkyl, and Cl₁₋₂₀ alkyl. Note that the first prefix may vary according to other limitations; for example, for unsaturated alkyl groups, the first prefix must be at least 2; for cyclic alkyl groups, the first prefix must be at least 3; etc.

Examples of (unsubstituted) saturated alkyl groups include, but are not limited to, methyl (C₁), ethyl (C₂), propyl (C₃), butyl (C₄), pentyl (C₅), hexyl (C₆), heptyl (C₇), octyl (C₈), nonyl (C₉), decyl (C₁₀), undecyl (C₁₁), dodecyl (C₁₂), tridecyl (C₁₃), tetradecyl (C₁₄), pentadecyl (C₁₅), and eicodecyl (C₂₀).

Examples of (unsubstituted) saturated linear alkyl groups include, but are not limited to, methyl (C₁), ethyl (C₂), n-propyl (C₃), n-butyl (C₄), n-pentyl (amyl) (C₅), n-hexyl (C₆), and n-heptyl (C₇).

Examples of (unsubstituted) saturated branched alkyl groups include, but are not limited to, iso-propyl (C₃), iso-butyl (C₄), sec-butyl (C₄), tert-butyl (C₄), iso-pentyl (C₅), and neo-pentyl (C₅).

Cycloalkyl: The term “cycloalkyl”, as used herein, pertains to an alkyl group which is also a cyclyl group; that is, a monovalent moiety obtained by removing a hydrogen atom from an alicyclic ring atom of a carbocyclic ring of a carbocyclic compound, which carbocyclic ring may be saturated or unsaturated (e.g. partially unsaturated, fully unsaturated), which moiety has from 3 to 20 carbon atoms (unless otherwise specified), including from 3 to 20 ring atoms. Preferably, each ring has from 3 to 7 ring atoms. Examples of groups of cycloalkyl groups include C₃₋₂₀ cycloalkyl, C₃₋₁₅ cycloalkyl, C₃₋₁₀ cycloalkyl, C₃₋₇ cycloalkyl.

Heterocyclyl: The term “heterocyclyl”, as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from a ring atom of a heterocyclic compound, which moiety has from 3 to 20 ring atoms (unless otherwise specified), of which from 1 to 10 are ring heteroatoms. Preferably, each ring has from 3 to 7 ring atoms, of which from 1 to 4 are ring heteroatoms.

In this context, the prefixes (e.g. C₃₋₂₀, C₃₋₇, C₅₋₆, etc.) denote the number of ring atoms, or range of number of ring atoms, whether carbon atoms or heteroatoms. For example, the term “C₅₋₆heterocyclyl”, as used herein, pertains to a heterocyclyl group having 5 or 6 ring atoms. Examples of groups of heterocyclyl groups include C₃₋₂₀ heterocyclyl, C₅₋₂₀ heterocyclyl, C₃₋₁₅ heterocyclyl, C₅₋₁₅ heterocyclyl, C₃₋₁₂ heterocyclyl, C₅₋₁₂ heterocyclyl, C₃₋₁₀ heterocyclyl, C₅₋₁₀ heterocyclyl, C₃₋₇ heterocyclyl, C₅₋₇ heterocyclyl, and C₅₋₆ heterocyclyl.

Examples of monocyclic heterocyclyl groups include, but are not limited to, those derived from:

N₁: aziridine (C₃), azetidine (C₄), pyrrolidine (tetrahydropyrrole) (C₅), pyrroline (e.g., 3-pyrroline, 2,5-dihydropyrrole) (C₅), 2H-pyrrole or 3H-pyrrole (isopyrrole, isoazole) (C₅), piperidine (C₆), dihydropyridine (C₆), tetrahydropyridine (C₆), azepine (C₇);

O₁: oxirane (C₃), oxetane (C₄), oxolane (tetrahydrofuran) (C₅), oxole (dihydrofuran) (C₅), oxane (tetrahydropyran) (C_(s)), dihydropyran (C₆), pyran (C₆), oxepin (C₇);

S₁: thiirane (C₃), thietane (C₄), thiolane (tetrahydrothiophene) (C₅), thiane (tetrahydrothiopyran) (C₆), thiepane (C₇);

O₂: dioxolane (C₅), dioxane (C₆), and dioxepane (C₇);

O₃: trioxane (C₆);

N₂: imidazolidine (C₅), pyrazolidine (diazolidine) (C₅), imidazoline (C₅), pyrazoline (dihydropyrazole) (C₅), piperazine (C₆);

N₁O₁: tetrahydrooxazole (C₅), dihydrooxazole (C₅), tetrahydroisoxazole (C₅), dihydroisoxazole (C₅), morpholine (C₆), tetrahydrooxazine (C₆), dihydrooxazine (C₆), oxazine (C₆);

N₁S₁: thiazoline (C₅), thiazolidine (C₅), thiomorpholine (C₆);

N2O₁: oxadiazine (C₆);

O₁S₁: oxathiole (C₅) and oxathiane (thioxane) (C₅); and,

N₁O₁S₁: oxathiazine (C₆).

Examples of substituted (non-aromatic) monocyclic heterocyclyl groups include those derived from saccharides, in cyclic form, for example, furanoses (C₅), such as arabinofuranose, lyxofuranose, ribofuranose, and xylofuranse, and pyranoses (C_(s)), such as allopyranose, altropyranose, glucopyranose, mannopyranose, gulopyranose, idopyranose, galactopyranose, and talopyranose.

R₁ and R² taken together with the nitrogen atom of the amide bond may represent a heterocyclyl group having at least one hydroxyl substituent. The heterocyclyl group may be a group selected from the N₁ examples provided above. The heterocyclyl group may contain one or more further heteroatoms. The heterocyclyl group may then be a group selected from the N₂, N₁O₁, N₁S₁, N₂O₁ and N₁O₁S₁ examples provided above.

Aryl: the term “aryl” as used herein, refers to a monovalent moiety obtained by removing a hydrogen atom from an aromatic ring atom of an aromatic compound, said compound having one ring, or two or more rings (e.g., fused).

Heteroaryl: The term “Heteroaryl” as used herein refers to an aryl group having one or more carbon atoms replaced with, but not limited to, a N, S, O heteroatom. In this case, a group may conveniently be referred to as a “C₅₋₂₀ heteroaryl” group, wherein “C₅₋₂₀” denotes ring atoms, whether carbon atoms or heteroatoms. Preferably, each ring has from 5 to 7 ring atoms, of which from 0 to 4 are ring heteroatoms.

Aralkyl: The term aralkyl as used herein, refers to an alkyl group, as defined above, substituted with one or more, preferably one, aryl groups as defined above.

Heteroaralkyl: The term ‘heteroaralky’ as used herein, refers to an alkyl group, as defined above, substituted with one or more, preferably one, aryl groups as defined above, where one or more carbon atoms in the alkyl and/or aryl group have been replaced with, but not limited to, a N, S, O heteroatom.

C₅₋₂₀ aryl: The term “C₅₋₂₀ aryl” as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from an aromatic ring atom of a C₅₋₂₀ aromatic compound and having from 5 to 20 ring atoms, and wherein at least one of said ring(s) is an aromatic ring. Preferably, each ring has from 5 to 7 ring atoms.

Examples of C₅₋₂₀ aryl groups which do not have ring heteroatoms (i.e. C₅₋₂₀ carboaryl groups) include, but are not limited to, those derived from benzene (i.e. phenyl) (C₆), naphthalene (C₁₀), anthracene (C₁₄), phenanthrene (C₁₄), and pyrene (C₁₆).

Examples of C₅₋₂₀ heteroaryl groups which comprise fused rings, include, but are not limited to, C₉ heteroaryl groups derived from benzofuran, isobenzofuran, benzothiophene, indole, isoindole; C₁₀ heteroaryl groups derived from quinoline, isoquinoline, benzodiazine, pyridopyridine; C₁₄ heteroaryl groups derived from acridine and xanthene.

The above groups, whether alone or part of another substituent, may themselves optionally be substituted with one or more groups selected from themselves and the additional substituents listed below.

Halo: —F, —CI, —Br, and —I.

Hydroxyl: —OH.

Ether: —OR, wherein R is an ether substituent, for example, a C₁₋₇ alkyl group (also referred to as a C₁₋₇alkoxy group), a C₃₋₂₀ heterocyclyl group (also referred to as a C₃₋₂₀ heterocyclyloxy group), or a C₅₋₂₀aryl group (also referred to as a C₅₋₂₀ aryloxy group), preferably a C₁₋₇ alkyl group.

Nitro: —NO₂.

Cyano (nitrile, carbonitrile): —CN.

Acyl (keto): —C(═O)R, wherein R is an acyl substituent, for example, H, a C₁₋₇ alkyl group (also referred to as C₁₋₇ alkylacyl or C₁₋₇ alkanoyl), a C₃₋₂₀ heterocyclyl group (also referred to as C₃₋₂₀ heterocyclylacyl), or a C₅₋₂₀ arylgroup (also referred to as C₅₋₂₀ arylacyl), preferably a C₁₋₇ alkyl group. Examples of acyl groups include, but are not limited to, —C(═O)CH₃ (acetyl), —C(═O)CH₂CH₃ (propionyl), —C(═O)C(CH₃)₃ (butyryl), and —C(═O)Ph (benzoyl, phenone).

Carboxy (carboxylic acid): —COOH.

Ester (carboxylate, carboxylic acid ester, oxycarbonyl): —C(═O)OR, wherein R is an ester substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of ester groups include, but are not limited to, —C(═O)OCH₃, —C(═O)OCH₂CH₃, —C(═O)OC(CH₃)₃, and —C(═O)OPh.

Amido(carbamoyl, carbamyl, aminocarbonyl, carboxamide): —C(═O)NR¹R², wherein R¹ and R² are independently amino substituents, as defined for amino groups. Examples of amido groups include, but are not limited to, —C(O)NH₂, —C(═O)NHCH₃, —C(═O)N(CH₃)₂, —C(═O)NHCH₂CH₃, and —C(═O)N(CH₂CH₃)₂, as well as amido groups in which R¹ and R², together with the nitrogen atom to which they are attached, form a heterocyclic structure as in, for example, piperidinocarbonyl, morpholinocarbonyl, thiomorpholinocarbonyl, and piperazinylcarbonyl.

Amino: —NR¹R², wherein R¹ and R² are independently amino substituents, for example, hydrogen, a C₁₋₇ alkyl group (also referred to as C₁₋₇ alkylamino or di-C₁₋₇ alkylamino), a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀aryl group, preferably H or a C₁₋₇ alkyl group, or, in the case of a “cyclic” amino group, R¹ and R², taken together with the nitrogen atom to which they are attached, form a heterocyclic ring having from 4 to 8 ring atoms. Examples of amino groups include, but are not limited to, —NH₂, —NHCH₃, —NHCH(CH₃)₂, —N(CH₃)₂, —N(CH₂CH₃)₂, and —NHPh. Examples of cyclic amino groups include, but are not limited to, aziridinyl, azetidinyl, pyrrolidinyl, piperidino, piperazinyl, perhydrodiazepinyl, morpholino, and thiomorpholino. In particular, the cyclic amino groups may be substituted on their ring by any of the substituents defined here, for example carboxy, carboxylate and amido.

Acylamido (acylamino): —NR¹C(═O)R², wherein R₁ is an amide substituent, for example, hydrogen, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably

H or a C₁₋₇ alkyl group, most preferably H, and R² is an acyl substituent, for example, a C₁₋₇alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of acylamide groups include, but are not limited to, —NHC(═O)CH₃, —NHC(═O)CH₂CH₃, and —NHC(═O)Ph. R₁ and R² may together form a cyclic structure, as in, for example, succinimidyl, maleimidyl, and phthalimidyl:

Aminocarbonyloxy: —OC(═O)NR¹R², wherein R¹ and R² are independently amino substituents, as defined for amino groups. Examples of aminocarbonyloxy groups include, but are not limited to, —OC(═O)NH₂, —OC(═O)NHMe, —OC(═O)NMe₂, and —OC(═O)NEt₂.

Ureido: —N(R¹)CONR²R³ wherein R² and R³ are independently amino substituents, as defined for amino groups, and R1 is a ureido substituent, for example, hydrogen, a C₁₋₇alkyl group, a C₃₋₂₀heterocyclyl group, or a C₅₋₂₀aryl group, preferably hydrogen or a C₁₋₇alkyl group. Examples of ureido groups include, but are not limited to, —NHCONH₂, —NHCONHMe, —NHCONHEt, —NHCONMe₂, —NHCONEt₂, —NMeCONH₂, —NMeCONHMe, —NMeCONHEt, —NMeCONMe₂, —NMeCONEt₂ and —NHCONHPh.

Guanidino: —NH—C(═NH)NH₂.

Tetrazolyl: a five membered aromatic ring having four nitrogen atoms and one carbon atom,

Imino: ═NR, wherein R is an imino substituent, for example, for example, hydrogen, a C₁₋₇alkyl group, a C₃₋₂₀heterocyclyl group, or a C₅₋₂₀aryl group, preferably H or a C₁₋₇alkyl group. Examples of imino groups include, but are not limited to, ═NH, ═NMe, and ═NEt.

Amidine (amidino): —C(═NR)NR₂, wherein each R is an amidine substituent, for example, hydrogen, a C₁₋₇alkyl group, a C₃₋₂₀heterocyclylgroup, or a C₅₋₂₀aryl group, preferably H or a C₁₋₇alkyl group. Examples of amidine groups include, but are not limited to, —C(═NH)NH₂, —C(═NH)NMe₂, and —C(═NMe)NMe₂.

Nitro: —NO₂.

Nitroso: —NO.

Azido: —N₃.

Cyano (nitrile, carbonitrile): —CN.

Isocyano: —NC.

Cyanato: —OCN.

Isocyanato: —NCO.

Thiocyano (thiocyanato): —SCN.

Acyloxy (reverse ester): —OC(═O)R, wherein R is an acyloxy substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of acyloxy groups include, but are not limited to, —OC(═O)CH₃ (acetoxy), —OC(═O)CH₂CH₃, —OC(═O)C(CH₃)₃, —OC(═O)Ph, —OC(═O)C₆H₄F, and —OC(═O)CH₂Ph.

Isothiocyano (isothiocyanato): —NCS.

Thiol: —SH.

Thioether (sulfide): —SR, wherein R is a thioether substituent, for example, a C₁₋₇alkyl group (also referred to as a C₁₋₇ alkylthio group), a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀aryl group, preferably a C₁₋₇ alkyl group. Examples of C₁₋₇ alkylthio groups include, but are not limited to, —SCH₃ and —SCH₂CH₃.

Disulfide: —SS—R, wherein R is a disulfide substituent, for example, a C₁₋₇alkyl group, a C₃₋₂₀heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group (also referred to herein as C₁₋₇alkyl disulfide). Examples of C₁₋₇alkyl disulfide groups include, but are not limited to, —SSCH₃ and —SSCH₂CH₃.

Sulfine (sulfinyl, sulfoxide): —S(═O)R, wherein R is a sulfine substituent, for example, a C₁₋₇alkyl group, a C₃₋₂₀heterocyclylgroup, or a C₅₋₂₀aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfine groups include, but are not limited to, —S(═O)CH₃ and —S(═O)CH₂CH₃.

Sulfoxide (sulfinyl): —S(═O)R, wherein R is a sulfoxide substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfoxide groups include, but are not limited to, —S(═O)CH₃ and —S(═O)CH₂CH₃.

Sulfonyl (sulfone): —S(═O)₂R, wherein R is a sulfone substituent, for example, a C₁₋₇alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀aryl group, preferably a C₁₋₇alkyl group. Examples of sulfone groups include, but are not limited to, —S(═O)₂CH₃ (methanesulfonyl, mesyl), —S(═O)₂CF₃, —S(═O)₂CH₂CH₃, and 4-methylphenylsulfonyl (tosyl).

Thioamido (thiocarbamyl): —C(═S)NR¹R², wherein R¹ and R² are independently amino substituents, as defined for amino groups. Examples of amido groups include, but are not limited to, —C(═S)NH₂, —C(═S)NHCH₃, —C(═S)N(CH₃)₂, and —C(═S)NHCH₂CH₃.

Sulfonamino: —NR¹S(═O)₂R¹ wherein R₁ is an amino substituent, as defined for amino groups, and R is a sulfonamino substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀heterocyclylgroup, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfonamino groups include, but are not limited to, —NHS(═O)₂CH₃, —NHS(═O)₂Ph and —N(CH₃)S(═O)₂C₆H₅.

Sulfinic acid (sulfino): —S(═O)OH, —SO₂H.

Sulfonic acid (sulfo): —S(═O)₂OH, —SO₃H.

Sulfinate (sulfinic acid ester): —S(═O)OR; wherein R is a sulfinate substituent, for example, a C₁₋₇alkyl group, a C₃₋₂₀heterocyclyl group, or a C₅₋₂₀aryl group, preferably a C₁₋₇alkyl group. Examples of sulfinate groups include, but are not limited to, —S(═O)OCH₃ (methoxysulfinyl; methyl sulfinate) and —S(═O)OCH₂CH₃ (ethoxysulfinyl; ethyl sulfinate).

Sulfonyloxy: —OS(═O)₂R, wherein R is a sulfonyloxy substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀heterocyclyl group, or a C₅₋₂₀aryl group, preferably a C₁₋₇alkyl group. Examples of sulfonyloxy groups include, but are not limited to, —OS(═O)₂CH₃ (mesylate) and —OS(═O)₂CH₂CH₃ (esylate).

Sulfate: —OS(═O)₂OR; wherein R is a sulfate substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfate groups include, but are not limited to, —OS(═O)₂OCH₃ and —SO(═O)₂OCH₂CH₃.

Sulfamyl (sulfamoyl; sulfinic acid amide; sulfinamide): —S(═O)NR¹R², wherein R¹ and R² are independently amino substituents, as defined for amino groups. Examples of sulfamyl groups include, but are not limited to, —S(═O)NH₂, —S(═O)NH(CH₃), —S(═O)N(CH₃)₂, —S(═O)NH(CH₂CH₃), —S(═O)N(CH₂CH₃)₂, and —S(═O)NHPh.

Sulfonamido (sulfinamoyl; sulfonic acid amide; sulfonamide): —S(═O)₂NR¹R², wherein R¹ and R² are independently amino substituents, as defined for amino groups. Examples of sulfonamido groups include, but are not limited to, —S(═O)₂NH₂, —S(═O)₂NH(CH₃), —S(═O)₂N(CH₃)₂, —S(═O)₂NH(CH₂CH₃), —S(═O)₂N(CH₂CH₃)₂, and —S(═O)₂NHPh.

Sulfamino: —NR¹S(═O)₂OH, wherein R¹ is an amino substituent, as defined for amino groups. Examples of sulfamino groups include, but are not limited to, —NHS(═O)₂OH and —N(CH₃)S(═O)₂OH.

Sulfonamino: —NR¹S(═O)₂R, wherein R¹ is an amino substituent, as defined for amino groups, and R is a sulfonamino substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀heterocyclyl group, or a C₅₋₂₀aryl group, preferably a C₁₋₇alkyl group. Examples of sulfonamino groups include, but are not limited to, —NHS(═O)₂CH₃ and —N(CH₃)S(═O)₂C₆H₅.

Sulfinamino: —NR¹S(═O)R, wherein R₁ is an amino substituent, as defined for amino groups, and R is a sulfinamino substituent, for example, a C₁₋₇alkyl group, a C₃₋₂₀heterocyclyl group, or a C₅₋₂₀aryl group, preferably a C₁₋₇alkyl group. Examples of sulfinamino groups include, but are not limited to, —NHS(═O)CH₃ and —N(CH₃)S(═O)C₆H₅.

Phosphino (phosphine): —PR₂, wherein R is a phosphino substituent, for example, —H, a C₁₋₇alkyl group, a C₃₋₂₀heterocyclylgroup, or a C₅₋₂₀aryl group, preferably —H, a C₁₋₇alkyl group, or a C₅₋₂₀aryl group. Examples of phosphino groups include, but are not limited to, —PH₂, —P(CH₃)₂, —P(CH₂CH₃)₂, —P(t-Bu)₂, and —P(Ph)₂.

Phospho: —P(═O)₂.

Phosphinyl (phosphine oxide): —P(═O)R₂, wherein R is a phosphinyl substituent, for example, a C₁₋₇alkyl group, a C₃₋₂₀heterocyclylgroup, or a C₃₋₂₀aryl group, preferably a C₁₋₇alkyl group or a C₅₋₂₀aryl group. Examples of phosphinyl groups include, but are not limited to, —P(═O)(CH₃)₂, —P(═O)(CH₂CH₃)₂, —P(═O)(t-Bu)₂, and —P(═O)(Ph)₂.

Phosphonic acid (phosphono): —P(═O)(OH)₂.

Phosphonate (phosphono ester): —P(═O)(OR)₂, where R is a phosphonate substituent, for example, —H, a C₁₋₇alkyl group, a C₃₋₂₀heterocyclylgroup, or a C₅₋₂₀aryl group, preferably —H, a C₁₋₇alkyl group, or a C₅₋₂₀aryl group. Examples of phosphonate groups include, but are not limited to, —P(═O)(OCH₃)₂, —P(═O)(OCH₂CH₃)₂, —P(═O)(O-t-Bu)₂, and —P(═O)(OPh)₂.

Phosphoric acid (phosphonooxy): —OP(═O)(OH)₂.

Phosphate (phosphonooxy ester): —OP(═O)(OR)₂, where R is a phosphate substituent, for example, —H, a C₁₋₇alkyl group, a C₃₋₂₀heterocyclylgroup, or a C₅₋₂₀aryl group, preferably —H, a C₁₋₇alkyl group, or a C₅₋₂₀aryl group. Examples of phosphate groups include, but are not limited to, —OP(═O)(OCH₃)₂, —OP(═O)(OCH₂CH₃)₂, —OP(═O)(O-t-Bu)₂, and —OP(═O)(OPh)₂.

Phosphorous acid: —OP(OH)₂.

Phosphite: —OP(OR)₂, where R is a phosphite substituent, for example, —H, a C₁₋₇alkyl group, a C₃₋₂₀heterocyclyl group, or a C₅₋₂₀aryl group, preferably —H, a C₁₋₇alkyl group, or a C₅₋₂₀aryl group. Examples of phosphite groups include, but are not limited to, —OP(OCH₃)₂, —OP(OCH₂CH₃)₂, —OP(O-t-Bu)₂, and —OP(OPh)₂.

Phosphoramidite: —OP(OR)²NR₂, where R¹ and R² are phosphoramidite substituents, for example, —H, a (optionally substituted) C₁₋₇alkyl group, a C₃₋₂₀heterocyclyl group, or a C₅₋₂₀aryl group, preferably —H, a C₁₋₇alkyl group, or a C₅₋₂₀aryl group. Examples of phosphoramidite groups include, but are not limited to, —OP(OCH₂CH₃)—N(CH₃)₂, —OP(OCH₂CH₃)—N(i-Pr)₂, and —OP(OCH₂CH₂CN)—N(i-Pr)₂.

Phosphoramidate: —OP(═O)(OR¹)—NR² ₂, where R¹ and R² are phosphoramidate substituents, for example, —H, a (optionally substituted) C₁₋₇alkyl group, a C₃₋₂₀heterocyclyl group, or a C₅₋₂₀aryl group, preferably —H, a C₁₋₇alkyl group, or a C₅₋₂₀aryl group. Examples of phosphoramidate groups include, but are not limited to, —OP(═O)(OCH₂CH₃)—N(CH₃)₂, —OP(═O)(OCH₂CH₃)—N(i-Pr)₂, and —OP(═O)(OCH₂CH₂CN)—N(i-Pr)₂.

Silyl: —SiR₃, where R is a silyl substituent, for example, —H, a C₁₋₇alkyl group, a C₃₋₂₀heterocyclyl group, or a C₅₋₂₀aryl group, preferably —H, a C₁₋₇alkyl group, or a C₅₋₂₀aryl group. Examples of silyl groups include, but are not limited to, —SiH₃, —SiNCH₃), —SiH(CH₃)₂, —Si(CH₃)₃, —Si(Et)₃, —Si(iPr)₃, —Si(tBu)(CH₃)₂, and —Si(tBu)₃.

Oxysilyl: —Si(OR)₃, where R is an oxysilyl substituent, for example, —H, a C₁₋₇alkyl group, a C₃₋₂₀heterocyclyl group, or a C₅₋₂₀aryl group, preferably —H, a C₁₋₇alkyl group, or a C₅₋₂₀aryl group. Examples of oxysilyl groups include, but are not limited to, —Si(OH)₃, —Si(OMe)₃, —Si(OEt)₃, and —Si(OtBu)₃.

Siloxy (silyl ether): —OSiR₃, where SiR₃ is a silyl group, as discussed above.

Oxysiloxy: —OSi(OR)₃, wherein OSi(OR)₃ is an oxysilyl group, as discussed above.

In many cases, substituents are themselves substituted.

As mentioned above, the groups that form the above listed substituent groups, e.g. alkyl, heterocyclyl and aryl, may themselves be substituted. Thus, the above definitions cover substituent groups which are substituted.

Preferred Compounds

Preferred compounds of the first aspect of the invention are described below.

Preferably, X1 is Leu, and X2 is Val or Ile; or X1 is Val, and X2 is Val or Ile. Most preferably, X1 is Leu, and X2 is Val; or X1 is Val, and X2 is Ile.

R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹ and R¹⁰ may be optionally substituted or optionally further substituted as appropriate. However, in some embodiments these groups are unsubstituted or not further substituted as appropriate.

Where R¹ or R² is an alkyl group, the alkyl group may be a C₁₋₇ alkyl group, most preferably a C₁₋₄ alkyl group. The R¹ or R² alkyl group is preferably fully saturated.

R¹ or R² may have one, two, three, four, five, six or seven carbon atoms.

Where R¹ and R² taken together with the nitrogen atom of the amide represent a heterocyclic group where the group further contains one or more heteroatoms, preferably the heteroatoms are not at neighbouring positions in the heterocyclic ring.

Where R¹ and R² taken together with the nitrogen atom of the amide represent a heterocyclic group where the group further contains one or more heteroatoms, the heterocyclic group is preferably a C₃₋₂₀ heterocyclic group. Preferably the heterocyclic group is a C₅₋₁₀ heterocyclic group. The heterocyclic group may have 5, 6 or 7 ring atoms.

Both R¹ and R² may have one or more hydroxyl substituents. Between them, R₁ and R² may have two or more hydroxyl substituents. Preferably, R¹ has one, two or three hydroxyl substituents.

R₁ and R² may be the same.

Preferably R¹ is an alkyl group. Preferably R² is hydrogen.

Where R¹ or R² is a heteroalkyl group having a hydroxyl substituent, the hydroxyl substituent is a substituent on a carbon atom of the heteroalkyl group.

Where R¹ or R² is an alkyl or heteroalkyl group having two or more hydroxyl substituents, each hydroxyl substituent is a substituent on a different carbon atom of the alkyl or heteroalkyl group.

In one embodiment, the R¹ or R² alkyl group is acyclic. In one embodiment, the R₁ or R² alkyl group is linear.

In one embodiment, R¹ or R² is substituted or further substituted as appropriate. The substituent may be one or more groups selected from the group consisting of: carboxy, ester, acyloxy, amido, acylamido, and aryl and heteroaryl. Preferably, the substituent is one or more groups selected from the group consisting of: carboxy, ester, acyloxy, aryl and heteroaryl.

Preferably R¹ or R² is independently one of the substituents given below, where * indicates the point of attachment to the nitrogen atom:

Additionally, or alternatively, R¹ or R² may be independently selected from one of the substituents given below, where * indicates the point of attachment to the nitrogen atom:

In one embodiment, R¹ is independently selected from one of the substituents given in either of the sets of substituents above. In this embodiment, R² is preferably hydrogen.

Alternatively, R₁ and R² together with the nitrogen atom, i.e. X, may be a substituent selected from the group below, where * indicates the point of attachment to the C-terminus carbonyl carbon:

Additionally, or alternatively, R₁ or R² may be independently selected from the substituent given below, where * indicates the point of attachment to the nitrogen atom:

Preferably R¹ is —CH₂CH₂OH.

In one embodiment, Z is —NH₂, an amino acid or —NR⁵COR⁶. Preferably, Z is —NH₂, or an amino acid.

In one embodiment, Z is —NR⁵COR⁶ and R⁵ is hydrogen.

Where Z is an amino acid residue, the amino acid residue is preferably a naturally occurring amino acid residue encoded by the genetic code or its D- isoform, more preferably an amino acid residue selected from the group Ile-, Lys-, Phe-, Val-, Glu-, Asp-, His-, Leu, Arg-, Ser- and Trp-. In one aspect, the amino acid residue may be selected from the group Ile-, Lys-, Phe-, Val-, Glu-, Asp-, His-, Leu-, Arg- and Ser-. Such variants may be produced by chemical addition of the residue to compounds where Z is —NH₂, as described in U.S. Pat. No. 6,022,851, which is incorporated herein by reference. It will be appreciated that the chemical addition of an amino acid allows the amino acid to be in the L- or D-configuration. This includes D-Ala, in addition to the D-forms of other amino acids such as those mentioned above.

The amino acid residue may a modified natural amino acid residue, such as those residues formed during the post-translational modification of, for example, serine, cytseine and threonine residues. A residue within the compound of the invention may be selected from the dehydrated amino acids shown in the group below:

The second of these structures may be referred to as a dehydroamino butyric acid residue. Additionally, an amino acid residue may be selected from the cyclic residues shown in the group below:

As will be appreciated, the synthesis of these cyclic structures typically involves the cyclisation of a serine, threonine or cysteine residue side chain with an amidic carbonyl of, typically, but not essentially, a neighbouring amino acid residue.

Thus, the structures shown above include a portion of a neighbouring group, such as a neighbouring amino acid. Alternatively, the neighbouring group may be derived from a group that together with a serine, threonine or cysteine residue forms an amide bond at the residue N-terminus. This is shown retrosynthetically in the example below for an oxazoline amino acid residue derived from a serine residue that is linked with a neighbouring group through an amide bond at the N-terminus of the serine residue:

The asterisk (*) indicates the location of the carbon atom in the oxazoline as derived from the carbonyl carbon in the neighbouring group. The retrosynthesis is presented for illustrative purposes only, and the post translationally modified amino acid residues discussed above may be prepared from alternative precursors.

The amino acid residue may be a non-natural or unusual natural amino acid. The amino acid may be selected from the group consisting of seleno serine, aminobutyric acid, aminoisobutyric acid, butlyglycine, citrulline, cyclohexylalanine, diaminopropionic acid, homoserine, hydroxy proline, norleucine, norvaline, ornithine, penicillaminepyroglutamic acid, sarcosine, statine, tetrahydroisoquinoline-3-carboxylic acid, and thienylalanine. The L- or D- forms may be selected.

The amino acid may be an α-, β-, or γ-amino acid. The amino group of the amino acid may be mono- or di-alkylated. Where Z is an amino acid residue, the amino group of the amino acid may be modified. Thus, the N terminus may be a group selected from —NR³R⁴, —NR⁵COR⁶, —NR⁵SOR⁶; —NR⁵SOR⁶, —NR⁵SO₂R⁶; —NR⁵C(S)NR⁶R⁷ and —NR⁵C(NR⁸)NR⁶R⁷ where R³, R⁴, R⁵, R⁶, R⁷ and R⁸ are defined as above.

Where Z is an amino acid residue, the amino acid residue may also be a protected amino acid residue. The amino group such protecting groups may be selected from the group consisting of Fmoc, Boc, Ac, Bn and Z (or Cbz). The side-chain may also be protected as appropriate. The side chains protecting groups may be selected from the group consisting of Pmc, Pbf, OtBu, Trt, Acm, Mmt, tBu, Boc, ivDde, 2-CITrt, tButhio, Npys, Mts, NO₂, Tos, OBzI, OcHx, Acm, pMeBzl, pMeOBz, OcHx, Born, Dnp, 2—Cl-Z, Bzl, For, and 2—Br-Z as appropriate for the side chain.

Natural and non natural amino acids, and their protected versions, as well as protecting group deprotection strategies are well known. Many are summarised in the Merck Novabiocher™ catalog ‘Reagents for Peptide and High-Throughput Synthesis’ (2006/7) (incorporated herein by reference in its entirety).

One of R³ and R⁴ may be a group, optionally substituted, selected from alkyl, heteroalkyl, aryl, heteroaryl, aralkyl and heteroaralkyl.

R³ and R⁴ may both be hydrogen.

Where Z is —NH₂, i.e. R³ and R⁴ are both hydrogen, this group may be in a protected form. The protecting group may be selected from the group consisting of Fmoc, Boc, Ac, Bn and Z (or Cbz). Alternative protecting groups may be used, such as those described below in relation to protected forms.

Preferably, R⁵ is hydrogen.

Preferably, Z is —NH₂, an amino acid or —NR⁵COR⁶. Where Z is —NR⁵COR⁶, preferably R⁵ is hydrogen and R⁶ is an aralkyl group substituted with a hydroxyl group, most preferably the aralkyl group is substituted on the alkyl portion of the group. R⁶ may be —CH(OH)Ph (i.e. Z is modified with a mandelyl group). R⁹ is preferably a group, optionally substituted, selected from alkyl, heteroalkyl, aryl, heteroaryl, aralkyl and heteroaralkyl.

The preferred compounds according to the first aspect of the invention present invention are the compounds listed below:

-   Compound I: Deoxy-Actagardine B N-[2-ethanolamine]monocarboxamide -   Compound II: Deoxy-Actagardine B N-[4-butanolamine]monocarboxamide -   Compound III: Actagardine N-[2-ethanolamine]monocarboxamide -   Compound IV: Deoxy-actagardine B (3-amino-1,2-propanediol)     monocarboxamide -   Compound V: Deoxy-actagardine B (2-amino-1,3-propanol)     monocarboxamide -   Compound VI: Deoxy-actagardine B     [tris(hydroxymethyl)methylamine]monocarboxamide -   Compound VII: Deoxy-actagardine B (1-amino-2-propanol)     monocarboxamide -   Compound VIII: Deoxy-actagardine B (1-amino-3-propanol)     monocarboxamide -   Compound IX: (L)-Phenylalanyl-(O)-deoxyactagardine B (ethanolamine)     monocarboxamide -   Compound X: (L)-Tryptophanyl-(O)-deoxyactagardine B (ethanolamine)     monocarboxamide -   Compound XI: (L)-Alanyl-(O)-deoxyactagardine B (ethanolamine)     monocarboxamide -   Compound XII: (D)-Alanyl-(O)-deoxyactagardine B (ethanolamine)     monocarboxamide -   Compound XIII: (L)-Isoleucinyl-(O)-deoxyactagardine B (ethanolamine)     monocarboxamide -   Compound XIV: (L)-Leucinyl-(O)-deoxyactagardine B (ethanolamine)     monocarboxamide -   Compound XV: N-Phenylacetyl deoxyactagardine B (ethanolamine)     monocarboxamide -   Compound XVI: N-Acetyl deoxyactagardine B (ethanolamine)     monocarboxamide -   Compound XVII: N-Mandelyl deoxyactagardine B (ethanolamine)     monocarboxamide -   Compound XVIII: Deoxyactagardine B (N,N-bis(2-hydroxyethyl)ethylene     diamine) monocarboxamide

Additionally, or alternatively the preferred compounds according to the first aspect of the invention present invention may be selected from the compounds listed below:

-   Compound XX: Deoxy-Actagardine B     N-[2-hydroxy-2-phenylethylamine]monocarboxamide -   Compound XXI: Deoxy-actagardine B (L-serine methyl ester)     monocarboxamide -   Compound XXII: Deoxyactagardine B     (N-(2-hydroxyethyl)ethylenediamine) monocarboxamide -   Compound XXIII: Deoxy-actagardine B (2-hydroxypiperazine)     monocarboxamide -   Additionally, or alternatively the preferred compounds according to     the first aspect of the invention present invention may be selected     from the compounds listed below: -   Compound XXX: (L)-Alanyl-(O)-deoxyactagardine B (ethanolamine)     monocarboxamide -   Compound XXXI: (D)-Alanyl-(O)-deoxyactagardine B (ethanolamine)     monocarboxamide -   Compound XXXII: (L)-Isoleucinyl-(O)-deoxyactagardine B     (ethanolamine) monocarboxamide -   Compound XXXIII: (L)-Leucinyl-(O)-deoxyactagardine B (ethanolamine)     monocarboxamide -   Compound XXXIV: N-Phenylacetyl deoxyactagardine B (ethanolamine)     monocarboxamide -   Compound XXXV: N-Acetyl deoxyactagardine B (ethanolamine)     monocarboxamide -   Compound XXXVI: N-Mandelyl deoxyactagardine B (ethanolamine)     monocarboxamide

The most preferred compounds are:

-   Compound I: Deoxy-Actagardine B N-[2-ethanolamine]monocarboxamide -   Compound III: Actagardine N-[2-ethanolamine]monocarboxamide

The most preferred compounds have improved antimicrobial activity in comparison to the actagardine and deoxyactagardine B compounds from which they are derived.

The present invention also provides variants, derivatives and precursors of the compounds of formula (I). These are described in detail below.

Variants

A variant of a compound of formula (I) includes a compound in which one or more, for example from 1 to 5, such as 1, 2, 3 or 4 amino acids are substituted by another amino acid. Preferably the amino acid is at a position selected from positions 2, 3, 4, 5, 8, 10, 11, 13, 15, 16 or 18 of the compound of formula (I).

Substitutions may be of one amino acid by another naturally occurring amino acid and may be conservative or non-conservative substitutions. Conservative substitutions include those set out in the following table, where amino acids on the same block in the second column and preferably in the same line in the third column may be substituted for each other:

ALIPHATIC Non-polar G A I L V Polar - uncharged C S T M N Q Polar - charged D E K R AROMATIC H F W Y

Alternatively, an amino acid may be substituted by one of the modified, non-natural or unusual amino acids described above.

A variant of a compound of the invention may include a compound where one or more crosslinks is a bridge other than a thionine bridge. Alternative bridges include, where appropriate, di-sulfide bridges, and amide and ester bridges (so-called macrolactam and macrolactone variants respectively).

Derivatives

Derivatives of compounds of the invention (including variants) are those in which one or more amino acid side chain of the compound of the invention has been modified, for example by esterification, amidation or oxidation.

Derivatives of compounds of the invention may be monoamide derivatives at one of the carboxy functions of actagardine. A derivative may include a compound in which the carboxy function of a side chain of an internal residue, e.g. that of the residue Glu11, is modified from —COOH to a group —COOR¹⁰ in which R¹⁰ represents hydrogen, (C₁-C₄)alkyl or (C₁-C₄)alkoxy (C₂-C₄)alkyl. Alternatively, the carboxy function of a side chain of an internal residue e.g. that of the residue Glu11, is modified from —COOH to a group —CONR¹R² where R¹ and R² are defined as above in relation to the C-terminus amide substituents.

Compound (I) is shown with crosslinks CROSSLINK 1-6, Lanthionine (Ser-Cys); CROSSLINK 7-12, Beta-methyllanthionine (Thr-Cys); and CROSSLINK 9-17, Beta-methyllanthionine (Thr-Cys). In one embodiment of the invention, one, two or three of these crosslinks may be thionine sulfoxide crosslinks.

Includes Other Forms

Included in the above compounds and polypeptide precursors are the well known ionic, salt, solvate, and protected forms. For example, a reference to carboxylic acid (—COON) also includes the anionic (carboxylate) form (—COO⁻), a salt or solvate thereof, as well as conventional protected forms. Similarly, a reference to an amino group includes the protonated form (—N⁺HR¹R²), a salt or solvate of the amino group, for example, a hydrochloride salt, as well as conventional protected forms of an amino group. Similarly, a reference to a hydroxyl group also includes the anionic form (—O−), a salt or solvate thereof, as well as conventional protected forms of a hydroxyl group.

For example, reference to the carboxylic acid-containing side chain of glutamic acid (Glu), which features as a residue in the compound of the invention, includes the carboxylate form. Where Z is —NH₂, reference to this group includes the protonated form of this amino group.

Isomers, Salts, Solvates, Protected Forms, and Prodrugs

Certain compounds may exist in one or more particular geometric, optical, enantiomeric, diasterioisomeric, epimeric, stereoisomeric, tautomeric, conformational, or anomeric forms, including but not limited to, cis- and trans-forms; E- and Z-forms; c-, t-, and r-forms; endo- and exo-forms; R-, S-, and meso-forms; D- and L-forms; d- and I-forms; (+) and (−) forms; keto-, enol-, and enolate-forms; syn- and anti-forms; synclinal- and anticlinal-forms; α- and β-forms; axial and equatorial forms; boat-, chair-, twist-, envelope-, and halfchair-forms; and combinations thereof, hereinafter collectively referred to as “isomers” (or “isomeric forms”).

For example, the amino acid residues described herein may exist in any one of the particular stereoisomeric forms. Similarly, the R¹ and R² groups may exist in any one of the particular stereoisomeric forms, where such forms exist. Likewise, the groups R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹ and R¹⁰ may exist in any one of the particular stereoisomeric forms, where such forms exist.

Where a compound or a precursor polypeptide of the invention includes a dihydroamino butyric acid residue, the residue may exist in either cis- or trans- forms.

If the compound is in crystalline form, it may exist in a number of different polymorphic forms.

Note that, except as discussed below for tautomeric forms, specifically excluded from the term “isomers”, as used herein, are structural (or constitutional) isomers (i.e. isomers which differ in the connections between atoms rather than merely by the position of atoms in space). For example, a reference to a methoxy group, —OCH₃, is not to be construed as a reference to its structural isomer, a hydroxymethyl group, —CH₂OH. Similarly, a reference to ortho-chlorophenyl is not to be construed as a reference to its structural isomer, meta-chlorophenyl. However, a reference to a class of structures may well include structurally isomeric forms falling within that class (e.g., C_(1-—), alkyl includes n-propyl and iso-propyl; butyl includes n-, iso-, sec-, and tert-butyl; methoxyphenyl includes ortho-, meta-, and para-methoxyphenyl).

The above exclusion does not pertain to tautomeric forms, for example, keto-, enol-, and enolate-forms, as in, for example, the following tautomeric pairs: keto/enol, imine/enamine, amide/imino alcohol, amidine/amidine, nitroso/oxime, thioketone/enethiol, N-nitroso/hyroxyazo, and nitro/aci-nitro.

Note that specifically included in the term “isomer” are compounds with one or more isotopic substitutions. For example, H may be in any isotopic form, including ¹H, ²H (D), and ³H(T); C may be in any isotopic form, including ¹²C¹³C, and ¹⁴C; O may be in any isotopic form, including ¹⁶O and ¹⁸O; and the like.

Unless otherwise specified, a reference to a particular compound includes all such isomeric forms, including (wholly or partially) racemic and other mixtures thereof. Methods for the preparation (e.g. asymmetric synthesis) and separation (e.g. fractional crystallisation and chromatographic means) of such isomeric forms are either known in the art or are readily obtained by adapting the methods taught herein, or known methods, in a known manner.

Unless otherwise specified, a reference to a particular compound also includes ionic, salt, solvate, and protected forms of thereof, for example, as discussed below, as well as its different polymorphic forms.

It may be convenient or desirable to prepare, purify, and/or handle a corresponding salt of the active compound, for example, a pharmaceutically-acceptable salt. Examples of pharmaceutically acceptable salts are discussed in Berge, et al., “Pharmaceutically Acceptable Salts”, J. Pharm. Sci, 66, 1-19 (1977).

For example, if the compound is anionic, or has a functional group which may be anionic (e.g., —COON may be —COO), then a salt may be formed with a suitable cation. Examples of suitable inorganic cations include, but are not limited to, alkali metal ions such as Na and K⁺, alkaline earth cations such as Ca²⁺ and Mg²⁺, and other cations such as API. Examples of suitable organic cations include, but are not limited to, ammonium ion (i.e., NH₄ ⁺) and substituted ammonium ions (e.g., NH₃R⁺, NH₂R₂ ⁺, NHR₃ ⁺, NR₄₊). Examples of some suitable substituted ammonium ions are those derived from: ethylamine, diethylamine, dicyclohexylamine, triethylamine, butylamine, ethylenediamine, ethanolamine, diethanolamine, piperazine, benzylamine, phenylbenzylamine, choline, meglumine, and tromethamine, as well as amino acids, such as lysine and arginine. An example of a common quaternary ammonium ion is N(CH₃)₄ ⁺.

If the compound is cationic, or has a functional group which may be cationic (e.g., —NH₂ may be —NH₃ ⁺), then a salt may be formed with a suitable anion. Examples of suitable inorganic anions include, but are not limited to, those derived from the following inorganic acids: hydrochloric, hydrobromic, hydroiodic, sulfuric, sulfurous, nitric, nitrous, phosphoric, and phosphorous. Examples of suitable organic anions include, but are not limited to, those derived from the following organic acids: acetic, propionic, succinic, gycolic, stearic, palmitic, lactic, malic, pamoic, tartaric, citric, gluconic, ascorbic, maleic, hydroxymaleic, phenylacetic, glutamic, aspartic, benzoic, cinnamic, pyruvic, salicyclic, sulfanilic, 2-acetyoxybenzoic, fumaric, toluenesulfonic, methanesulfonic, ethanesulfonic, ethane disulfonic, oxalic, isethionic, valeric, and gluconic. Examples of suitable polymeric anions include, but are not limited to, those derived from the following polymeric acids: tannic acid, carboxymethyl cellulose.

It may be convenient or desirable to prepare, purify, and/or handle a corresponding solvate of the active compound. The term “solvate” is used herein in the conventional sense to refer to a complex of solute (e.g. active compound, salt of active compound) and solvent. If the solvent is water, the solvate may be conveniently referred to as a hydrate, for example, a mono-hydrate, a di-hydrate, a tri-hydrate, etc.

It may be convenient or desirable to prepare, purify, and/or handle the active compound in a chemically protected form. The term “chemically protected form,” as used herein, pertains to a compound in which one or more reactive functional groups are protected from undesirable chemical reactions, that is, are in the form of a protected or protecting group (also known as a masked or masking group or a blocked or blocking group). By protecting a reactive functional group, reactions involving other unprotected reactive functional groups can be performed, without affecting the protected group; the protecting group may be removed, usually in a subsequent step, without substantially affecting the remainder of the molecule. See, for example, “Protective Groups in Organic Synthesis” (T. Green and P. Wuts; 3rd Edition; John Wiley and Sons, 1999).

For example, an amine group may be protected as described previously where Z is —NH₂ above. Additionally, an amine group may be protected as an amide or a urethane, for example, as: a methyl amide (—NHC0—CH₃); a benzyloxy amide (—NHCO—OCH₂C₆H₅, —NH-Cbz); as a t-butoxy amide (—NHCO—OC(CH₃)₃, —NH-Boc); a 2-biphenyl-2-propoxy amide (—NHCO—OC(CH₃)₂C₆H₄C₆H₅, —NH-Bpoc), as a 9-fluorenylmethoxy amide (—NH-Fmoc), as a 6-nitroveratryloxy amide (—NH-Nvoc), as a 2-trimethylsilylethyloxy amide (—NH-Teoc), as a 2,2,2-trichloroethyloxy amide (—NH-Troc), as an allyloxy amide (—NH-Alloc), as a 2(-phenylsulphonyl)ethyloxy amide (—NH-Psec); or, in suitable cases, as an N-oxide (>NO.).

For example, a carboxylic acid group may be protected as described previously in relation to the amino acid residues above. For example, a carboxylic acid group may be protected as an ester for example, as: a C_(1-—), alkyl ester (e.g. a methyl ester; a t-butyl ester); a C₁₋₇haloalkyl ester (e.g. a C₁₋₇-trihaloalkyl ester); a triC₁₋₇alkylsilyl-C₁₋₇alkyl ester; or a C₅₋₂₀aryl-Cl₁₋₇alkyl ester (e.g. a benzyl ester; a nitrobenzyl ester); or as an amide, for example, as a methyl amide.

For example, a hydroxyl group may be protected as an ether (—OR) or an ester (—OC(═O)R), for example, as: a t-butyl ether; a benzyl, benzhydryl (diphenylmethyl), or trityl (triphenylmethyl)ether; a trimethylsilyl or t-butyldimethylsilyl ether; or an acetyl ester (—OC(═O)CH₃, —OAc).

For example, an aldehyde or ketone group may be protected as an acetal or ketal, respectively, in which the carbonyl group (>C=O) is converted to a diether (>C(OR)₂), by reaction with, for example, a primary alcohol. The aldehyde or ketone group is readily regenerated by hydrolysis using a large excess of water in the presence of acid.

It may be convenient or desirable to prepare, purify, and/or handle the active compound in the form of a prodrug. The term “prodrug”, as used herein, pertains to a compound which, when metabolised (e.g. in vivo), yields the desired active compound. Typically, the prodrug is inactive, or less active than the active compound, but may provide advantageous handling, administration, or metabolic properties.

For example, some prodrugs are esters of the active compound (e.g. a physiologically acceptable metabolically labile ester). During metabolism, the ester group (—C(═O)OR) is cleaved to yield the active drug. Such esters may be formed by esterification, for example, of any of the carboxylic acid groups (—COON) in the parent compound, with, where appropriate, prior protection of any other reactive groups present in the parent compound, followed by deprotection if required. Examples of such metabolically labile esters include, but are not limited to, those wherein R is C₁₋₂₀ alkyl (e.g.-Me, -Et); C₁₋₇aminoalkyl (e.g. aminoethyl; 2-(N,N-diethylamino)ethyl; 2-(4-morpholino)ethyl); and acyloxy-C₁₋₇alkyl (e.g. acyloxymethyl; acyloxyethyl; e.g. pivaloyloxymethyl; acetoxymethyl; 1-acetoxyethyl; 1-(1-methoxy-1-methyl)ethyl-carbonxyloxyethyl; 1-(benzoyloxy)ethyl; isopropoxy-carbonyloxymethyl; 1-isopropoxy-carbonyloxyethyl; cyclohexyl-carbonyloxymethyl; 1-cyclohexyl-carbonyloxyethyl; cyclohexyloxy-carbonyloxymethyl; 1-cyclohexyloxy-carbonyloxyethyl; (4-tetrahydropyranyloxy) carbonyloxymethyl; 1-(4-tetrahydropyranyloxy)carbonyloxyethyl; (4-tetrahydropyranyl)carbonyloxymethyl; and 1-(4-tetrahydropyranyl)carbonyloxyethyl).

Further suitable prodrug forms include phosphonate and glycolate salts. In particular, hydroxy groups (—OH), can be made into phosphonate prodrugs by reaction with chlorodibenzylphosphite, followed by hydrogenation, to form a phosphonate group —O—P(═O)(OH)₂. Such a group can be cleaved by phosphatase enzymes during metabolism to yield the active drug with the hydroxy group.

Also, some prodrugs are activated enzymatically to yield the active compound, or a compound which, upon further chemical reaction, yields the active compound. For example, the prodrug may be a sugar derivative or other glycoside conjugate, or may be an amino acid ester derivative.

Methods for Preparing Compounds of the Invention

The inventors have previously described methods for the preparation of lantibiotic compounds, as well as derivatives and variants, and precursors thereof. The inventors' co-pending earlier application PCT/GB2007/000138 (WO/2007/083112) is hereby incorporated by reference in its entirety. The compounds described in this document may be used as starting materials for the compounds described in the present invention.

Particular reference is made to the following sections in the inventors' co-pending application:

-   -   Expression Construct;     -   Recombinant Expression Vector;     -   Expression Cassettes;     -   Expression Libraries;     -   Host Cell including ‘Lantibiotic-producing host cell’ and         ‘Non-producer cell’;     -   Production of Compounds of the Invention; and     -   Examples 1-4 and 7.

The compounds described herein may be used as starting materials for the synthesis of other compounds for use in the invention.

The actagardine compounds for use in the invention may be prepared from known actagardine compounds. Preferably, the actagardine compounds of the invention are prepared from actagardine, actagardine B and deoxyactagardine B. These antibiotics may be referred to as a ‘parent lantibiotic’ or a ‘lantibiotic starting material’.

An actagardine compound may be produced by expression of a nucleic acid, for example in the form of an expression construct encoding a precursor polypeptide carried in a recombinant expression vector, in a host cell which carries an appropriate lantibiotic gene, such as the LanA gene, together with, where necessary, associated cluster genes required for conversion of a precursor polypeptide to an actagardine compound. Variant actagardine compounds may be produced by appropriate modification of the LanA gene using methods known per se in the art.

The LanO gene, which has been identified as part of the actagardine gene cluster, is thought to encode the protein responsible for the oxidation of the deoxy-form of actagardine compounds to actagardine in which Y is —S(O)—. Modification of this gene may allow the production of derivative compounds having an alternative crosslinked structure. Modification of the LanO gene also allows the relative levels of oxidized (Y═S(O)) and reduced (Y═S—) forms of the compounds produced in the host cell to be altered.

The LanM gene, which has also been identified as part of the actagardine gene cluster, is thought to encode the protein required for the conversion of a precursor polypeptide to a lantibiotic compound. Modulation of this gene, and other genes encoding modification proteins, may allow the production of derivative compounds having an alternative crosslinked structure. Modulation of these genes may also allow the production of compounds having or retaining an amino acid sequence attached to the N-terminus of the actagardine compound, such as a leader sequence.

Typically, those compounds produced by cell culture will have a free amine N-terminus (i.e. z is —NH₂) and a free carboxylic acid C-terminus (i.e. X is —OH). These termini may be derivatised as described in more detail below. Where an actagarine compound has a modified N-terminus, the starting material will typically have a free amine N-terminus. It will be appreciated that the compounds produced by cell culture may have a modified N-terminus. Thus, a compound for use as a starting material may include a compound where Z is —NHR³, where R³ is defined according to the compounds of formula (I).

Where the invention relates to the use of compounds derived from an actagardine compound starting material in which X1 and X2 represent Leu and Val respectively, the host cell may be A. liguriae NCIMB 41362 without any further modification.

Where host cells produce a mixture of starting material compounds, e.g. those in which Y is —S— or —S(O)—, the products may be isolated using standard separation techniques such as HPLC, e.g. as described in U.S. Pat. No. 6,022,851 for the production of Actagardine and Ala-Actagardine.

Following culture of the cell, the lantibiotic starting material may be recovered from the host cell culture unmodified. The recovered and modified compounds may be formulated in the form of a pharmaceutical composition, optionally in the form of a pharmaceutically acceptable salt.

Alternatively, the lantibiotic starting material, or the precursors, variants and derivatives thereof, may be obtained by chemical peptide synthesis, for example solid-phase peptide synthesis (SPPS). Such techniques are well known in the art. Preferably, the lantibiotic starting material is obtained from cell culture.

The compounds of the invention may be in substantially isolated form. Isolated compounds of the invention will be those as defined above in isolated form, free or substantially free of material with which it is associated such as polypeptides from which the compounds are derived. The compounds may of course be formulated with diluents or adjuvants and still for practical purposes be isolated.

A compound of the invention may also be in a substantially purified form, in which case it will generally comprise the compound in a preparation in which more than 90%, e.g. 95%, 98% or 99% of the compound in the preparation is a compound of the invention.

The compounds of the invention are prepared by reacting a lantibiotic starting material having a carboxyl C-terminus with a 2 to 6-fold molar excess of an appropriate amino alkyl or amino heteroalkyl group, in a suitable organic solvent such as dimethylformamide at a temperature typically between 0° C. and room temperature and in the presence of a suitable condensing agent. Representative examples of condensing agents are carbodiimide derivatives such as dicyclohexylcarbodiimide, phosphoazidates such as DPPA or benzotriazole-based coupling reagents such as PyBop™, HATU or TBTU.

Compounds of the invention where Z is an amino acid or —NR⁵COR⁶ may be prepared from a lantiobiotic starting material having an amino group N-terminus by means of a coupling reaction with an appropriate carboxylic acid in the presence of a condensing agent such as dicyclohexylcarbodiimide, phosphoazidates such as DPPA or benzotriazole-based coupling reagents such as PyBop™, HATU or TBTU. An organic amine base, such as triethylamine or diisopropylethylamine is generally added to expedite the reaction.

Alternatively, preformed activated derivatives of the appropriate acid, such as the pentafluorophenyl esters, may be used as reagents to react with the lantibiotic N-terminus. A catalyst, such as HOBt may be added to expedite the reaction. The solvent is typically DMF.

Where the carboxylic acid being coupled to the lantibiotic contains further functional groups that may interfere with the coupling reaction, suitable protection groups familiar to those skilled in the art may be employed. For example, Fmoc or tBoc protection groups may be employed for amino acid derivatives to be coupled to the N-terminus of the lantibiotic.

Compounds of the invention where Z is —NR³R⁴ may be prepared from a lantibiotic having an amino group N-terminus by means of a coupling reaction with an aldehyde or ketone in an organic solvent, such as dichloromethane, dimethylsulphoxide or acetic acid, in the presence of a suitable reducing agent, such as sodium borohydride or sodium triacetoxyborohydride. Such reducing agent may be used in solution or bound to a suitable resin, such as polystyrene. Depending on the reaction conditions, the aldehyde or ketone employed and the ratio of the reagents employed in the reaction, both mono- and di-alkylation of the N-terminus are possible. Alternatively, the reaction may be performed without a reducing agent. In which case it is possible to obtain compounds of the invention where Z is —N═R⁹.

Compounds of the invention where Z is —NR⁵C(O)OR⁶; —NR⁵SOR⁶, —NR⁵SO₂R⁶; —NR⁵C(S)NR⁶R⁷ or —NR⁵C(NR⁸)NR⁶R⁷ may be prepared from a lantiobiotic starting material having an amino group N-terminus by means of a coupling reaction with an appropriately activated substituent group reagent. Thus, compounds where Z is —NR⁵C(O)OR⁶, may be prepared using CIC(O)OR⁶ and such like. Similarly, compounds where Z is —NR⁵SO₂R⁶ may be additional functionality that is protected with a protecting group. The protecting group may be removed after the coupling reaction as appropriate.

The compounds of the invention where Z is other than —NH₂ (i.e. compounds where R³ and R⁴ are not hydrogen) may be prepared from starting materials that are modified at either the C- or N-terminus. The other terminus may then be modified to provide the compounds of the invention. Thus, the sequence of substitutions can either feature N-terminal modification followed by C-terminal modification, or vice versa. Where issues of regioselectivity arise, for instance where the C-terminal substituent features an amino group, a suitable protection strategy may be employed.

Thus, a lantibiotic starting material where the N-terminus of the compound is an amino acid residue, —NR³R⁴, —NR⁵COR⁶, —NR⁵C(O)OR⁶; —NR⁵SOR⁶, —NR⁵SO₂R⁶, —NR⁵C(S)NR⁶R⁷, —NR⁵C(NR⁸)NR⁶R⁷, or —N═R⁹ (as defined previously in relation to the compounds of the invention), may equally be coupled with amino alcohols at the C-terminal.

The inventors have observed that under the coupling conditions used to couple an amino alcohol to the carboxyl C-terminus of a parent lantibiotic, the carboxyl group of a side chain amino acid residue, such as glutamic acid, may also be modified. Such compounds where both the C-terminus and a side chain of an amino acid are modified are also within the scope of the present invention. Appropriate manipulation of the reaction conditions may be used to modify the amount of product obtained where the side chain of an amino acid has been modified. Alternatively a protection and deprotection strategy may be employed to ensure that the side chain is not modified. Suitable amino acid residue side chain protecting groups are well known and include the protecting groups mentioned above.

Reaction products may be identified by LC-MS. Reaction progression may be monitored by HPLC. See, for example, FIG. 3. HPLC may be used to monitor the consumption of the starting material, the appearance of the product and the production of side or decomposition products (if any).

The products and the starting material may be analysed by NMR spectroscopy. Such techniques have been described previously by the present inventors in PCT/GB2007/000138 (WO/2007/083112). The structure of the product lantiobiotic-based compound may be confirmed using standard techniques such as COSY, HMBC, TOCSY, HSQC and NOESY, as well as NOE techniques.

Pharmaceutically Acceptable salt

A “pharmaceutically acceptable salt”, may be an acid addition salt in which the base retains the biological effectiveness and properties of the compound and which is physiologically acceptable. Such salts include those formed with inorganic acids such as hydrochloric acid, hydrobromic acid, sulphuric acid, nitric acid, phosphoric acid and the like, and organic acids such as acetic acid, propionic acid, glycolic acid, pyruvic acid, oxalic acid, malic acid, malonic acid, succinic acid, maleic acid, fumaric acid, tartaric acid, citric acid, benzoic acid, cinnamic acid, mandelic acid, methanesulfonic acid, ethanesulfonic acid, p-toluenesulfonic acid, salicylic acid and the like.

Salts also include basic salts, such as an alkali or alkaline earth metal salt, e.g. a sodium, potassium, calcium or magnesium salt.

Additionally, or alternatively salts may be formed with any one of N-methyl-D-glutamine, L-arginine, L-tysine, choline, and tris(hydroxymethyl)aminomethane.

Pharmaceutical Compositions

The lantibiotic-based compounds of the present invention may be formulated together with one or more other pharmaceutically acceptable ingredients well known to those skilled in the art, including, but not limited to, pharmaceutically acceptable carriers, adjuvants, excipients, diluents, fillers, buffers, preservatives, anti-oxidants, lubricants, stabilizers, solubilisers, surfactants (e.g., wetting agents), masking agents, colouring agents, flavouring agents, and sweetening agents. The formulation may further comprise other active agents, for example, other therapeutic or prophylactic agents. Thus, the present invention further provides pharmaceutical compositions, as defined above, and methods of making a pharmaceutical composition comprising admixing at least one active compound, as defined above, together with one or more other pharmaceutically acceptable ingredients well known to those skilled in the art, e.g., carriers, adjuvants, excipients, etc. If formulated as discrete units (e.g., tablets, etc.), each unit contains a predetermined amount (dosage) of the active compound.

The term “pharmaceutically acceptable” as used herein pertains to compounds, ingredients, materials, compositions, dosage forms, etc., which are, within the scope of sound medical judgement, suitable for use in contact with the tissues of the subject in question (e.g., human) without excessive toxicity, irritation, allergic response, or other problem or complication, commensurate with a reasonable benefit/risk ratio. Each carrier, adjuvant, excipient, etc. must also be “acceptable” in the sense of being compatible with the other ingredients of the formulation.

Compositions may be formulated for any suitable route and means of administration.

Pharmaceutically acceptable carriers or diluents include those used in formulations suitable for oral, rectal, nasal, topical (including buccal and sublingual), vaginal or parenteral (including subcutaneous, intramuscular, intravenous, intradermal, intrathecal and epidural) administration. The formulations may conveniently be presented in unit dosage form and may be prepared by any of the methods well known in the art of pharmacy. Such methods include the step of bringing into association the active ingredient with the carrier which constitutes one or more accessory ingredients. In general the formulations are prepared by uniformly and intimately bringing into association the active ingredient with liquid carriers or finely divided solid carriers or both, and then, if necessary, shaping the product.

For solid compositions, conventional non-toxic solid carriers include, for example, pharmaceutical grades of mannitol, lactose, cellulose, cellulose derivatives, starch, magnesium stearate, sodium saccharin, talcum, glucose, sucrose, magnesium carbonate, and the like may be used. The active compound as defined above may be formulated as suppositories using, for example, polyalkylene glycols, acetylated triglycerides and the like, as the carrier. Liquid pharmaceutically administrable compositions can, for example, be prepared by dissolving, dispersing, etc, an active compound as defined above and optional pharmaceutical adjuvants in a carrier, such as, for example, water, saline aqueous dextrose, glycerol, ethanol, and the like, to thereby form a solution or suspension. If desired, the pharmaceutical composition to be administered may also contain minor amounts of non-toxic auxiliary substances such as wetting or emulsifying agents, pH buffering agents and the like, for example, sodium acetate, sorbitan monolaurate, triethanolamine sodium acetate, sorbitan monolaurate, triethanolamine oleate, etc. Actual methods of preparing such dosage forms are known, or will be apparent, to those skilled in this art; for example, see “Remington: The Science and Practice of Pharmacy”, 20th Edition, 2000, pub. Lippincott, Williams & Wilkins. The composition or formulation to be administered will, in any event, contain a quantity of the active compound(s) in an amount effective to alleviate the symptoms of the subject being treated.

Dosage forms or compositions containing active ingredient in the range of 0.25 to 95% with the balance made up from non-toxic carrier may be prepared.

For oral administration, a pharmaceutically acceptable non-toxic composition is formed by the incorporation of any of the normally employed excipients, such as, for example, pharmaceutical grades of mannitol, lactose, cellulose, cellulose derivatives, sodium crosscarmellose, starch, magnesium stearate, sodium saccharin, talcum, glucose, sucrose, magnesium, carbonate, and the like. Such compositions take the form of solutions, suspensions, tablets, pills, capsules, powders, sustained release formulations and the like. Such compositions may contain 1%-95% active ingredient, more preferably 2-50%, most preferably 5-8%.

Parenteral administration is generally characterized by injection, either subcutaneously, intramuscularly or intravenously. Injectables can be prepared in conventional forms, either as liquid solutions or suspensions, solid forms suitable for solution or suspension in liquid prior to injection, or as emulsions. Suitable excipients are, for example, water, saline, dextrose, glycerol, ethanol or the like. In addition, if desired, the pharmaceutical compositions to be administered may also contain minor amounts of non-toxic auxiliary substances such as wetting or emulsifying agents, pH buffering agents and the like, such as for example, sodium acetate, sorbitan monolaurate, triethanolamine oleate, triethanolamine sodium acetate, etc.

For topical applications, the pharmaceutically acceptable compositions may be formulated in a suitable ointment or gel containing the active component suspended or dissolved in one or more carriers. Carriers for topical administration of the compounds of this invention include, but are not limited to, mineral oil, liquid petrolatum, white petrolatum, propylene glycol, polyoxyethylene, polyoxypropylene compound, emulsifying wax and water. Alternatively, the pharmaceutically acceptable compositions can be formulated in a suitable lotion or cream containing the active components suspended or dissolved in one or more pharmaceutically acceptable carriers. Suitable carriers include, but are not limited to, mineral oil, sorbitan monostearate, polysorbate 60, cetyl esters wax, cetearyl alcohol, 2-octyldodecanol, benzyl alcohol and water.

The percentage of active compound contained in such parental or topical compositions is highly dependent on the specific nature thereof, as well as the activity of the compound and the needs of the subject. However, percentages of active ingredient of 0.1% to 10% w/w employable, and will be higher if the composition is a solid which will be subsequently diluted to the above percentages. Preferably, the composition will comprise 0.2-2% w/w of the active agent in solution.

Further teaching regarding suitable carriers, adjuvants, excipients, etc. can be found in standard pharmaceutical texts, for example, “Remington: The Science and Practice of Pharmacy”, 20th Edition, 2000, pub. Lippincott, Williams & Wilkins; and Handbook of Pharmaceutical Excipients, 2nd edition, 1994.

Administration of Compounds

Lantibiotic-based compounds and compositions of the invention may be administered to a subject in a method of medical treatment or prophylaxis. The subject may be a human or animal subject. The animal subject may be a mammal, or other vertebrate.

Thus there is provided a compound of the invention for use in a method of treatment or prophylaxis of a subject. There is also provided use of a compound of the invention for the manufacture of a medicament for use in a method of treatment or prophylaxis of a subject.

Particularly, the compounds of the invention may be used to treat a microbial, typically a bacterial, infection in a subject

The term “microbial infection” refers to the invasion of the host animal by pathogenic microbes. This includes the excessive growth of microbes that are normally present in or on the body of an animal. More generally, a microbial infection can be any situation in which the presence of a microbial population(s) is damaging to a host animal. Thus, an animal is “suffering” from a microbial infection when excessive numbers of a microbial population are present in or on an animal's body, or when the presence of a microbial population(s) is damaging the cells or other tissue of an animal.

The infection may be an infection of the gastrointestinal tract, preferably the intestine, and most preferably of the colon. Particularly, in one aspect of the present invention, there is provided a method of treating a bacterial infection. Preferably, the infection is a Clostridium infection, preferably a Clostridium perfringens, Clostridium difficile, Clostridium tetani or Clostridium botulinum infection, most preferably C. difficile infection. These methods provide new and useful alternatives to the method of treatment utilising a type-A lantibiotic, vancomycin or metronidazole.

The bacterial infection may be an Enterococcus sp, Streptococcus spp, Staphylococcus spp. or Clostridium difficile infection.

The invention also provides a method for treating of a disease caused by a bacterial infection of the intestine, and preferably the colon. The method may be used to treat pseudomembranous colitis or Clostridium difficile-associated diarrhoea (CDAD). Preferably, the infection is a Clostridium infection, preferably a Clostridium perfringens, Clostridium difficile, Clostridium tetani or Clostridium botulinum infection, most preferably C. difficile infection.

The present invention also provides a method of treatment or prophylaxis of a subject comprising the step of administering a compound or composition of the invention to the subject. Preferably the compound or composition is administered orally.

The present invention also relates to the treatment or prophylaxis of a Clostridium difficile, Helicobacter pylori or vancomycin-resistant enterococci (VRE) infection. Preferably the invention relates to a Clostridium difficile infection.

The present invention also relates to the treatment of an infection that has not been eradicated by treatment with another active compound, preferably a compound that is not a type-B lantibiotic. The other active compound may be vancomycin.

Where compound of the present invention is administered to a subject having an infection that has not been eradicated by treatment with another active compound, the type-B lantibiotic may be administered within 1 day, 1 week or 1 month of the last administration of the other active compound.

The compounds and compositions may also be used for systemic treatment of bacteraemia (including catheter related bacteraemia), pneumonia, skin and skin structure infections (including surgical site infections), endocarditis and osteomyelitis. These and other such treatments may be directed against causative agents such as staphylococci, streptococci, enterococci. The compounds of the invention or compositions thereof may also be used for topical treatment of skin infections including acne i.e. Propionibacterium acnes. The compounds and compositions thereof may also be used in the treatment of eye infections, such as conjunctivitis.

The compounds may also be used in the treatment or prevention of infection of the skin in wounds or burns. In addition, the compounds and compositions described herein for use in the invention may be used in prophylactic methods. This may be practiced on subjects at risk of infection (e.g. patients entering a hospital) or on health professionals or other carers at risk of being carriers of such infections.

Most preferably, the compounds and compositions may be used for treatment of gut super-infection, such as that caused by Clostridium difficile including multiply-resistant C. difficile (pseudomembranous colitis). The compound or composition may be administered orally. Gut infections associated with Helicobacter pylori may also be treated.

The present invention also provides a method for treating CDAD. Complete relief of symptoms of CDAD by the end of the treatment may be defined as resolution to less than 3 bowel movements per day (whether formed or unformed), and no associated fever, elevated WBC (white blood cell) count, or abdominal pain.

The method of treatment may be of a bacterial infection, including a skin, mucosal, enteric or systemic infection.

The compounds according to the invention can be administered enterally (orally), parenterally (intramuscularly or intravenously), rectally, vaginally, or locally (topically). They can be administered in the form of solutions, powders (tablets, capsules including microcapsules), ointments (creams or gel), or suppositories. Possible auxiliaries for formulations of this type-Are the pharmaceutically customary liquid or solid fillers and extenders, solvents, emulsifiers, lubricants, flavor corrigents, colorants and/or buffer substances.

As an expedient dose, 0.1-1,000, preferably 0.2-100, mg/kg of body weight are administered. They are expediently administered in dose units which contain at least the efficacious daily amount of the compounds according to the invention, e.g. 30-3,000, preferably 50-1,000, mg. Preferably, the effective amount of the compound to be administered is from around 100 to around 2,000 mg per patient per day.

The experimental basis of the present invention, including its best mode, will now be further described in detail, by way of example only, with reference to the accompanying drawings.

Synthesis of Lantiobiotic-Based Compounds

The following compounds were made, in which the parent lantibiotic, and the groups X1, X2, Z, and R₁ and R² were as follows:

Compound Lantibiotic X1 X2 Y Z R¹ R² I Deoxy- actagardine B Leu Val —S— —NH₂

H II Deoxy- actagardine B Leu Val —S— —NH₂

H III Actagardine Val Ile —S(O)— —NH₂

H IV Deoxy- actagardine B Leu Val —S— —NH₂

H V Deoxy- actagardine B Leu Val —S— —NH₂

H VI Deoxy- actagardine B Leu Val —S— —NH₂

H VII Deoxy- actagardine B Leu Val —S— —NH₂

H VIII Deoxy- actagardine B Leu Val —S— —NH₂

H XVIII Deoxy- actagardine B Leu Val —S— —NH₂

H IX Deoxy- actagardine B Leu Val —S— -Phe

H X Deoxy- actagardine B Leu Val —S— -Tyr

H

The asterisk indicates the point where R¹ is attached to the nitrogen atom that is linked to alanine residue at position 19 via an amide bond.

The following compounds were also made, in which the parent lantibiotic, and the groups X1, X2, Z, and R¹ and R² were as follows:

Compound Lantibiotic X1 X2 Y Z R¹ R² XX Deoxy- actagardine B Leu Val —S— —NH₂

H XXI Deoxy- actagardine B Leu Val —S— —NH₂

H XXII Deoxy- actagardine B Leu Val —S— —NH₂

H XXIII Deoxy- actagardine B Leu Val —S— —NH₂

H

Preparation of Compounds I-VIII, XVIII, and XX-XXIII General Procedure 1

To a solution of lantiobiotic (e.g. actagardine, actagardine B, or deoxy-actagardine B) (200 mg, 108 nmol), an appropriate aminoalcohol (330 nmol) and diisopropylethylamine (410 nmol) in dry dimethylformamide (2 ml) was added portionwise a solution of benzotriazole-1-yl-oxy-tris-pyrrolidino-phosphonium hexafluorophosphate (PyBop™) (125 mg, 258 nmol) in dry dimethylformamide (1.5 ml). The mixture was analysed by HPLC to follow the progress of the reaction, adding further aliquots of the PyBop™ solution until all the starting material had been consumed. HPLC analysis at this stage also showed variable amounts (5-20%) of the diamide (see FIG. 3). After completion of the reaction, the mixture was diluted with 30% acetonitrile in 20 mM Kpi aqueous phosphate buffer, pH7 (10 ml) and the monoamide was purified by preparative HPLC using the conditions described in Table 1 The appropriate fractions were concentrated to 25% of their original volume and desalted by loading on to a preconditioned C18 Bond Elut column (500 mg) which was subsequently washed by sequential elution with two column volumes of 30, 40, 70 and 90% aqueous methanol. Evaporation of the appropriate fractions gave the desired products as white solids. Samples were analysed by LC-MS using the conditions described below.

TABLE 1 Preparative HPLC conditions for the separation of lantiobiotic (e.g. actagardine, actagardine B, or deoxy-actagardine B) and aminoalcohol derivatised product. Column Capitol HPLC Ltd C18 - BDS - HL5 - 26052 15 cm × 20 mm Solvent A 30% Acetonitrile in 20 mM Potassium Phosphate pH 7.0 Solvent B 65% Acetonitrile in 20 mM Potassium Phosphate pH 7.0 Detection 268 nm Flow Rate 10 ml/min Time (T) = 0 min 100% A T = 1 min 100% A T = 19 min 25% B T = 20 min 100% B T = 25 min 100% B T = 26 min 100% A T = 30 min 100% A Collection Start 8 min; End 20 min; 1 minute fractions

Compound I: Deoxy-Actagardine B N-[2-ethanolamine]monocarboxamide

Was obtained from coupling of deoxyactagardine B and ethanolamine according to General Procedure 1. Yield 18 mg, 85% yield. [M+2H 2⁺] calculated 979.0. found 980.2.

Compound II: Deoxy-Actagardine B N-[4-butanolamine]monocarboxamide

Was obtained from coupling of deoxyactagardine B and butanolamine according to General Procedure 1. Yield 9 mg, 43% yield. [M+2H 2⁺] calculated 972.50. found 979.9.2

Compound III: Actagardine N-[2-ethanolamine]monocarboxamide

Was obtained from coupling of deoxyactagardine B and ethanolamine according to General Procedure 1. Yield 11 mg, 53% yield. [M+2H 2⁺] calculated 966.5. found 966.1

Compound IV: Deoxy-Actagardine B (3-amino-1,2-propanediol) monocarboxamide

Was obtained from coupling of deoxyactagardine B and 3-amino-1,2-propanediol according to General Procedure 1. Yield 18 mg, 87% yield. [M+2H 2⁺] calculated 973.5.0. found 973.9

Compound V: Deoxy-Actagardine B (2-amino-1,3-propanol) monocarboxamide

Was obtained from coupling of deoxyactagardine B and 2-amino-1,3-propanol according to General Procedure 1. Yield 20 mg, 96% yield. [M+2H 2⁺] calculated 973.5. found 973.9

Compound VI: Deoxy-Actagardine B [tris(hydroxymethyl)methylamine]monocarboxamide

Was obtained from coupling of deoxyactagardine B and tris(hydroxymethyl)methylamine according to General Procedure 1. Yield 13 mg, 69% yield. [M+2H 2^(+]) calculated 988.5. found 988.6

Compound VII: Deoxy-Actagardine B (1-amino-2-propanol) monocarboxamide

Was obtained from coupling of deoxyactagardine B and 1-amino-2-propanol according to General Procedure 1. Yield 16 mg, 78% yield. [M+2H 2₊] calculated 965.5. found 965.6

Compound VIII: Deoxy-Actagardine B (1-amino-3-propanol) monocarboxamide

Was obtained from coupling of deoxyactagardine B and 1-amino-3-propanol according to General Procedure 1. Yield 19 mg, 87% yield. [M+2H 2+] calculated 965.5. found 965.3

Compound XVIII: Deoxyactagardine B (N,N-bis(2-hydroxyethyl)ethylene diamine) monocarboxamide

Was obtained from coupling of deoxyactagardine B and N,N-bis(2-hydroxyethyl)ethylene diamine according to General Procedure 1. Yield 48%. [M+2H 2+] calculated 1002.0. found 1002.3

Compound XX: Deoxy-Actagardine B N-[2-hydroxy-2-phenylethylamine]monocarboxamide

Was obtained from coupling of deoxyactagardine B and N-[2-hydroxy-2-phenylethylamine] according to General Procedure 1. [M+2H 2₊] calculated 995.5. found 995.8.

Compound XXI: Deoxy-actagardine B (L-serine methyl ester) monocarboxamide

Was obtained from coupling of deoxyactagardine B and L-serine methyl ester according to General Procedure 1. [M+2H 2⁺] calculated 987.5. found 986.9.

Compound XXII: Deoxyactagardine B (N-(2-hydroxyethyl)ethylenediamine) monocarboxamide

Was obtained from coupling of deoxyactagardine B and N-(2-hydroxyethyl)ethylenediamine according to General Procedure 1. [M+2H 2⁺] calculated 980. found 979.8.

Compound XXIII: Deoxy-actagardine B (2-hydroxypiperazine) monocarboxamide

Was obtained from coupling of deoxyactagardine B and 2-hydroxypiperazine according to General Procedure 1. [M+2H 2⁺] calculated 978.5. found 977.7.

Preparation of Compounds IX and X

General Procedure 2 exemplified for (L)-Tryptophanyl-(O)-deoxyactagardine B N-(9-Fluorenylmethoxycarbonyl)-tryptophan-O-pentafluorophenyl ester (80 mg, 135 nmol) was added to a solution of 1-hydroxybezotriazole hydrate (18 mg, 135 nm) in dry dimethylformamide (1 ml). The mixture was then added to a solution of deoxyactagardine B (50 mg, 27 nmol) in dry dimethylformamide (0.5 ml). The mixture was left at room temperature for 15 min, after which all the starting material had been consumed. Water (0.05 ml) and piperidine (0.1 ml) were added and the mixture was left at room temperature for 1 h. The reaction mixture was diluted into 30% aqueous methanol and the resulting white suspension loaded on to a 1 g C18 solid phase extraction cartridge. Material was eluted with fractions of 40%, 50%, 60% and 70% aqueous methanol. The 60% fraction was evaporated to dryness, leaving a tan solid. Yield=35 mg (63%) [M+2H²⁺] calculated 1030.0. found 1030.1

Compound X: (L)-Tryptophanyl-(O)-deoxyactagardine B (ethanolamine) monocarboxamide

Was obtained from coupling of (L)-Tryptophanyl-(O)-deoxyactagardine B (50 mg) and ethanolamine according to General Procedure 1. Yield 23 mg, 45% yield. [M+2H 2₂₊] calculated 1051.5. found 1051.8

(L)-Phenylalanyl-(O)-deoxyactagardine B

Was obtained from the coupling of deoxyactagardine B and N-(9-Fluorenylmethoxycarbonyl)-phenylalanine-O-pentafluorophenyl ester according to General Procedure 2. Yield 65% yield. [M+2H²⁺] calculated 1010.5. found 1011.0

Compound IX: (L)-Phenylalanyl-(O)-deoxyactagardine B (ethanolamine) monocarboxamide

Was obtained from coupling of (L)-Phenylalanyl-(O)-deoxyactagardine B (50 mg) and ethanolamine according to General Procedure 1. Yield 23 mg, 45% yield. [M+2H²⁺] calculated 1032.0. found 1032.2

Compounds XI-XVIII and XXX-XXXVI may be prepared in a similar manner to the methods which are described above.

High Performance Liquid Chromatography

HPLC analyses were performed using a Hewlett Packard 1050 series HPLC system with the parameters as described below:

Column: Zorbax SB-C18, 4.6×150 mm, 5μ

Mobile Phase A: 30% Acetonitrile in 20 mM potassium phosphate buffer pH 7.0

Mobile Phase B: 65% Acetonitrile in 20 mM potassium phosphate buffer pH 7.0

Flow rate: 1 ml/min

Gradient:

Time 0 min 100% A  0% B Time 10 min  0% A 100% B Time 11 min  0% A 100% B Time 11.2 min 100% A  0% B Cycle time 15 min Injection volume: 10 μl

Detection: 210 nm

High performance liquid chromatography-mass spectrometry (HPLC-MS)

HPLC-MS analyses were performed on a Hewlett Packard™ 1050 series HPLC system linked to a Micromass™ Platform LC (operated with MassLynx™ version 3.5 software) with the following parameters:

Column: Agilent Zorbax™ SB-C18 150×4.6 mm 5μ

Flow rate: 1 ml/min

Mobile phase: A 10% acetonitrile, 0.1% formic acid 90% water.

-   -   B 90% acetonitrile, 0.1% formic acid, 90% water.     -   Linear gradient A to B over 10 minutes, hold 1 min, B-A

Wavelength: 200-400 nm

Injection volume: 10 μl

Post column split: 1:10

Mass spectrometer: Micromass™ Platform LC Mode: Electrospray positive

Nitrogen flow: 380 l/hr

Capillary voltage: 40V

Skimmer lens offset: 5V

Example 1 Solubility of Alcoholamine Derivatives

Typically, compounds of the invention were isolated using phosphate buffers. The water solubility of deoxyactagardine B was measured at 4.5 g/l, whereas the aqueous solubility of the corresponding ethanolamide derivative Compound I was measured at 15 g/1.

Example 2 Antibacterial Activity of Alcoholamine Derivatives

The compounds of the invention show antimicrobial activity in vitro and in vivo. They are most active against Enterococci spp, Streptococci spp and Clostridium difficile (Tables 2-4A) and some derivatives have improved activity compared to the parent lantibiotic.

Susceptibility testing for all aerobic organisms with the exception of Streptococcus pneumoniae was performed by two-fold serial antibiotic dilutions in Mueller-Hinton Broth supplemented with 50 μg/ml Ca²⁺ unless otherwise noted. Susceptibility testing for S. pneumoniae was performed by two-fold serial antibiotic dilutions in Brain-Heart-Infusion Broth supplemented with 50 μg/ml Ca²⁺ unless otherwise noted. Actively growing broth cultures were diluted to contain 10⁵ to 10⁶CFU/ml by adjusting to an OD600 of 0.2-0.3. They were then diluted a further 1:100 in fresh sterile broth. The assays were performed in duplicate in sterile 96-well microtitre plates in a total volume of 200 μl (160 μl broth, 20 μl antimicrobial agent, 20 μl inoculum) in a concentration range from 64 μg/ml to 0.06 μg/ml. Plates were incubated aerobically, with shaking, for 18-20 hours at 37° C. with the minimum inhibitory concentration (MIC) defined as the lowest concentration of drug that prevented visible growth. Clinical isolates of Clostridium difficile were tested in Wilkins-Chalgren Anaerobe Agar under anaerobic conditions. In all cases, vancomycin was used as a reference antibiotic

TABLE 2 MIC data (μg/ml) for actagardine, deoxy-actagardine B, vancomycin and compounds I-VIII against a panel of common pathogens: Compound Micro organism Acta. Deoxyacta. B I II III IV V VI VII VIII Vanc. E. faecium >64 64 8 >64 64 >64 >64 64 >64 >64 >64 7131121 E. faecium 16 32 16 32 16 16 16 16 16 16 4 19579 E. faecalis 4 32 4 8 4 32 32 32 8 16 4 29212 S. aureus 32 8 4 8 16 32 32 32 32 32 1 R33 S. aureus 16 32 4 8 8 16 16 16 16 32 2 SH1000 S. epidermis 32 16 8 8 32 64 64 64 64 64 2 11047 M. luteus 1 1 0.25 8 1 8 16 16 16 32 2 4698 S. pneumoniae 4 4 2 8 4 16 16 16 64 64 >64 R6

In the table above, Acta. refers to actagardine, Deoxyacta. B refers to deoxyactagardine-B, and Vanc. refers to vancomycin.

TABLE 3 MIC data (μg/ml) for actagardine, deoxy-actagardine B and compounds I and II against a panel of Staphyloccus, enterococci and streptococci. Deoxyacta- Actagardine gardine-B I III Vancomycin intermediate Staphyloccus aureus S. aureus V99 32   32   32 16 S. aureus MI >32 >32   32 32 S. aureus Mu3 32   32   32 32 S. aureus 26 32   32 >32 32 S. aureus Mu50 32   32 >32 32 S. aureus 2 32   32   32 32 S. aureus NJ >32 >32 >32 >32 Methicillin resistant Staphyloccus aureus S. aureus 12232 16   16   32 8 S. aureus R36 16   16   16 16 S. aureus R34 16   16   16 8 S. aureus R39 32    32, >32 >32 S. aureus R40 32   32   32 32 S. aureus W71 32   32 >32 32 S. aureus W74 32   32   32 32 S. aureus W96 32   32  >32, >32 S. aureus W97 32   32 >32 >32 S. aureus W98 16   16   32 32 S. aureus W99 >32 >32   32 32 Methicillin sensitive Staphyloccus aureus S. aureus G15 >32 >32 >32 >32 S. aureus G20 32   32 >32 32 S. aureus G22 32   32 >32 32 S. aureus G23 32   32 >32 32 S. aureus G28 16   16   32 16 S. aureus G30 32   32 >32 32 S. aureus G31 >32 >32 >32 >32 S. aureus G32 32   32 >32 32 S. aureus G33 32   32 >32 32 S. aureus G35 32   32 >32 >32 S. aureus SH1000 16   16   32 16 Methicillin sensitive Staphylococcus epidermidis S. epidermidis >32 >32 >32 >32 GRL05001 S. epidermidis >32 >32 >32 >32 GRL05002 S. epidermidis 32   32 >32 32 GRL05003 S. epidermidis >32 >32 >32 32 GRL05004 S. epidermidis >32 >32 >32 >32 GRL05005 S. epidermidis >32 >32 >32 >32 GRL05006 S. epidermidis >32   32 >32 >32 GRL05007 S. epidermidis >32 >32 >32 >32 GRL05008 S. epidermidis >32 >32 >32 >32 GRL05009 S. epidermidis >32 >32 >32 >32 GRL05010 Methicillin resistant Staphylococcus epidermidis S. epidermidis >32 >32 >32 >32 7755298 S. epidermidis >32 >32 >32 >32 7865688 S. epidermidis >32 >32 >32 >32 7753921 S. epidermidis >32 >32 >32 >32 GRL05011 S. epidermidis >32 >32 >32 >32 GRL05013 S. epidermidis >32 >32 >32 >32 GRL05014 S. epidermidis >32 >32 >32 >32 GRL05015 S. epidermidis >32 >32 >32 >32 GRL05017 S. epidermidis >32 >32 >32 >32 GRL05019 S. epidermidis 32   32   32 32 GRL05020 Vancomycin sensitive enterococci E. faecalis 7754422 32   32    8 8 E. faecium 7865229 >32 >32 >32 >32 E. faecium 19579 16   16   32 16 E. faecalis GRL05022 16   16   16 ,8 E. faecalis GRL05023 8    8    8 8 E. faecalis GRL05024 16   16    8 8 E. faecalis GRL05026 16   16   16 8 E. faecalis GRL05027 8    8   16 8 E. faecalis GRL05029 8    8   16 4 E. faecalis GRL05030 8    8    8 4 Vancomycin resistant enterococci E. faecium 7662769 >32 >32 >32 >32 E. faecium 7634337 >32 >32 >32 >32 E. faecium 7865532 >32 >32 >32 >32 E. faecium 9709024 >32 >32 >32 >32 E. faecium GRL05031 4    4    4 4 E. faecium GRL05032 4    4    4 4 E. faecium 9710577 >32 >32 >32 >32 E. faecium GRL05033 8    8    8 8, 4 E. faecium GRL05034 32, 16 32, 16 >32 16 E. faecium GRL05035 32, 16 32, 16 >32 16 Streptococcus pyogenes S. pyogenes 7755441 ≦0.5  ≦0.5  ≦0.5 ≦0.5 S. pyogenes 7713283 1  ≦0.5    1 ≦0.5 S. pyogenes 7865844 ≦0.5  ≦0.5  ≦0.5 ≦0.5 S. pyogenes 7755255 ≦0.5  ≦0.5  ≦0.5 ≦0.5 S. pyogenes 7755584 ≦0.5  ≦0.5    1 ≦0.5 S. pyogenes ≦0.5  ≦0.5    1 ≦0.5 GRL05045 S. pyogenes 7865253 ≦0.5  ≦0.5  ≦0.5 ≦0.5 S. pyogenes 7865289 ≦0.5  ≦0.5    1 ≦0.5 S. pyogenes ≦0.5  ≦0.5    1 ≦0.5 GRL05041 S. pyogenes ≦0.5  ≦0.5  ≦0.5 ≦0.5 GRL05042 Viridans streptococci S. mitis 1 7722543 8    8    8 4 S. oralis 7862912.1 8    8   32 8 S. mitis 1 7863547 4    4    4 4 S. salivarius 2    2    1 1 GRL05064 S. constellatus >32 >32 >32 >32 GRL05065 S. mitis GRL05062 8    8   16 8 S. mitis GRL05067 16   16     8 16 S. acidominimus 4    4    4 4 7862865

TABLE 4 MIC data (μg/ml) for actagardine, deoxy-actagardine B, vancomycin and compounds I-VIII against Clostridium difficile Clostridium difficile Acta. Deoxyacta. B I II III IV V VI VII VIII Vanc. C. difficile 4 4 2 — 2 2 — — 2 2 1 37779 C. difficile 4 4 2 — 2 2 4 4 4 2 1 19126 C. difficile 4 4 2 — 2 — — — — — 1 B32 C. difficile 4 4 2 — 2 — — — — — 1 E16 C. difficile 2 4 1 — 1 — — — — — 1 E4 C. difficile 4 4 1 — 2 — — — — — 1 P24 C. difficile 1 4 0.5 — 1 — — — — — 0.5 027C C. difficile 2 4 0.5 — 1 — — — — — 0.5 027SM C. difficile 2 4 1 — 1 — — — — — 0.5 P49 C. difficile 2 4 2 — 1 — — — — — 1 P59 C. difficile 2 4 0.5 — 1 — — — — — 0.5 P62 C. difficile 4 4 2 — 2 — — — — — 1 E101

In the table above, Acta. refers to actagardine, Deoxyacta. B refers to deoxyactagardine-B, and Vanc. refers to vancomycin.

In addition, compounds XX-XXIII were tested against Clostridium difficile, and the MIC data is given below.

TABLE 4A Activity of Type-B lantibiotics Against C. difficile Clostridium difficile L LI LII LIII C. difficile 2 4 2 4 19126 C. difficile 2 4 2 4 37779 C. difficile 2 2 2 4 027C C. difficile 2 4 2 2 630

Example 3 In Vivo Efficacy of Type-B Antibiotics in the Hamster Model of C. difficile Associated Cecitis

The in vivo efficacy of two of the compounds of the invention (compounds I and III) in the treatment of C.difficile infections was evaluated in the standard animal model for CDAD, clindamycin induced cecitis in the hamster. The results are summarised in FIGS. 1 and 2.

In the first experiment (FIG. 1) groups of 6 animals were dosed with approximately 10⁷ cells of C. difficile strain VPI 10463 and 24 hours later with a subcutaneous dose of 10 mg/kg clindamycin phosphate. After a further 24 h, the groups were then treated either with vehicle, vancomycin or compound III three times daily at 50 mg/kg/day.

The procedure as described induced a C.difficile infection in the test animals, from which all animals treated only with vehicle died within 3 days. In contrast, all animals treated with vancomycin or compound III survived for the duration of the entire 5-day dosing period, demonstrating the protective effects of this compound.

In a second experiment (FIG. 2), groups of 6 hamsters were first dosed with a subcutaneous dose of 10 mg/kg clindamycin phosphate, followed 24 h later with approximately 10⁷ cells of C. difficile strain ATCC BAA-1382. After a further 24 h, the groups were then treated either with vehicle, vancomycin or compound I three times daily at 50 mg/kg/day. The procedure described for the second experiment allows the establishment of a C. difficile infection from which the animal may be rescued by an effective antibiotic. As FIG. 2 demonstrates, compound I was equally effective in rescuing the animals as the currently accepted clinical standard, vancomycin.

Example 4 Activity of Type-B Lantibiotics Against Other Gut Organisms

The compounds provided herein may have improved selectivity for pathogenic bacteria compared to vancomycin. These compounds may have improved selectivity for Clostridium difficile over gut flora, such as Bifidobacterium spp and Bacteroides spp.

The activities of several compounds (deoxyactagardine, vancomycin and compound III) against a number of species commonly occurring as part of the gut flora were measured and compared with vancomycin (Table 5). The compounds were found to have low potency against Bifidobacterium spp and Bacteroides spp and it can therefore fairly be assumed that they would have no significant effect on the gut flora at therapeutic doses levels, unlike vancomycin.

TABLE 5 Activity of Type-B Lantibiotics Against Organisms Common in the Intestinal Flora. Minimal Inhibitory Concentration (MIC) μg/ml Deoxyacta- Organism gardine B III Vancomycin E. coli DC2 >64 >64 >64 (membrane more susceptible) E. coli >64 >64 >64 ATCC 25922 E. faecium (VSE) 64 16 0.5 ATCC 19579 E. faecium (VSE) 8 4 4 ATCC 29212 E. coli DC2 >64 >64 >64 (membrane more susceptible) E. faecium (VRE) >64 64 >64 (clinical isolate) E. faecium (VRE) 4 4 >64 (clinical isolate) Bifidobacterium adolescentis 16 32 1 NCTC 11814 Bifidobacterium longum 16 32 1-2 NCTC 11818 Bacteroides fragilis >64 >64 32 NCTC 9343 Bacteroides thetaiotaomicron >64 >64 64 NCTC 10582

Example 5 Stability of Type-B Lantibiotics in Simulated Gastric and Intestinal Fluids

The lantibiotic-based compounds provided herein may have increased stability to enzymatic degradation compared to type-A lantibiotics, such as nisin. Particularly, the compounds may have improved stability to intestinal juices compared to type-A lantibiotics.

Nisin, mersacidin, compound I and compound III were tested for their susceptibility towards enzymatic digestion in the stomach. Nisin, mersacidin and compound III were tested for their susceptibility towards enzymatic digestion in the intestine. The SGF and SIF were based on the standard USP solutions for simulated gastric and simulated intestinal fluids and their activity confirmed against Bovine Serum Albumin (Hilger et al, Clin. Exp. Immunol. 2001, 123, 387-94). The compounds were incubated in SGF or SIF at 37° C. and their concentrations quantified by analytical HPLC (UV detection at 210 nm). The potential degradation of each compound was also monitored qualitatively by measuring in vitro antibacterial activity against Micrococcus luteus.

FIG. 4 shows the concentration of (a) nisin and mersacidin and (b) compounds I and III as a function of time in Simulated Gastric Fluid. The compounds tested did not show appreciable degradation in SGF.

In contrast, FIG. 5 (a) shows that nisin was rapidly degraded in SIF with a half-life of approximately 15 minutes. The rapid degradation of nisin in this medium supports the observation that the clinical utility of nisin for the treatment of colonic infections is very limited unless the compound can be protected from degradative enzymes by means of careful formulation.

FIG. 5 (b) also shows that compound III is essentially stable in SIF and that for these compounds metabolic instability is unlikely to be a factor affecting their efficacy in treating colonic C. difficile infections. The concentration data obtained by HPLC was corroborated by in vitro activity against M. luteus, which remained unaltered for mersacidin and deoxyactagardine B during the course of the experiment.

Example 6 In Vivo Stability of Type-B Antibiotics

For the purpose of treating intestinal Clostridium difficile infections with an orally administered, non-absorbed antibiotic it is of great importance that the compound is resistant to digestive enzymes and metabolism by the intestinal flora such that high concentrations can be achieved at the site of infection, typically the colon. Whilst in vitro models of gastric and intestinal fluids can provide an early indication of GI stability of a compound, in vivo experiments may provide more direct evidence that the compound reached the site of infection. In the

Male Sprague-Dawley rats were dosed with compound I at 100 mg/kg via the oral route. Faeces and urine were collected over a 48 h period in two batches (at 24 h and 48 h post dose). Blood samples were taken at various time points for the first 24 h.

Analysis of the various biological samples for the parent compound showed that at least 35% of compound I was excreted in faeces unchanged, demonstrating that high colonic concentrations of the type-B antibiotic can be achieved. No material was recovered from plasma or urine after oral dosing, a result consistent with low GI absorption.

It will be apparent to those skilled in the art that various modifications and variations can be made in the methods and compositions of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

REFERENCES

The following references are incorporated by reference herein in their entirety:

-   U.S. Pat. No. 6,022,851 -   PCT/G 82007/000138 (WO/2007/083112) -   Berge, et al., J. Pharm. Sci 1997, 66, 1-19 -   Chatterjee, Paul, Xie and van der Donk, Chem. Rev. 2005, 105, 633 -   Hilger et al, Clin. Exp. Immunol. 2001, 123, 387-94 -   van Kraaij, de Vos, Siezen and Kuipers, Nat. Prod. Rep. 1999, 16,     575 -   Parenti, Pagani, Beretta, J. Antibiotics 1976, 29, 501 -   Sahl and Bierbaum Annual Rev. Microbiol. 1998, 52, 41-79 -   Zimmerman, Metzger and Jung, Eur. J. Biochem. 1995, 228, 786 -   Merck Novabiochem™ catalog ‘Reagents for Peptide and High-Throughput     Synthesis’ (2006/7) “Remington: The Science and Practice of     Pharmacy”, 20th Edition, 2000, pub. Lippincott, Williams & Wilkins     “Protective Groups in Organic Synthesis” (T. Green and P. Wuts; 3rd     Edition; John Wiley and Sons, 1999) 

1.
 1. A compound of the formula:

wherein: X1 denotes that the residue is Leu; Val; or Ile; X2 denotes that the residue is Leu; Val; or Ile; R₁ represents an alkyl or heteroalkyl group, substituted by at least one hydroxyl substituent, and R² represents hydrogen, or an alkyl or heteroalkyl group, optionally substituted by at least one hydroxyl substituent, or R¹ and R² taken together with the nitrogen atom represent a heterocyclic group having at least one hydroxyl substituent, wherein the heterocyclic group optionally further contains one or more heteroatoms; Z is an amino acid residue, —NR³R⁴, —NR⁵COR⁶, —NR⁵C(O)OR⁶; —NR⁵SOR⁶, —NR⁵SO₂R⁶; —NR⁵C(S)NR⁶R⁷, —NR⁵C(NR⁸)NR⁶R⁷, or —N═R⁹, where R³, R⁴, R⁵, R⁶, R⁷, R⁸ and R⁹ are independently hydrogen, or a group, optionally substituted, selected from alkyl, heteroalkyl, aryl, heteroaryl, aralkyl and heteroaralkyl, with the proviso that R⁹ is not hydrogen; Y is —S— or —S(O)—; or a pharmaceutically acceptable salt thereof.
 2. A compound according to claim 1, wherein Z is —NH₂, an amino acid or —NR⁵COR⁶.
 3. A compound according to claim 1 or claim 2, wherein Z is an amino acid selected from the group Ala, Ile-, Lle, Lys-, Phe-, Val-, Glu-, Asp-, His-, Leu-, Arg-, Ser- and Trp- and said amino acids are in the D- or L- configuration.
 4. A compound according to claim 2, wherein Z is —NR⁵COR⁶ and R⁵ is hydrogen.
 5. A compound according, claim 1 wherein R² is hydrogen.
 6. A compound according to claim 1, wherein X1 is Leu, and X2 is Val or Ile; or X1 is Val, and X2 is Val or Ile.
 7. A compound according to claim 1, wherein R¹ is a C₁₋₇ alkyl group substituted by at least one hydroxyl substituent.
 8. A compound according to claim 1, wherein R¹ has one, two or three hydroxyl group substituents.
 9. A compound according to claim 1, wherein R¹ is selected from the group consisting of:

wherein * indicates the point of attachment to the nitrogen atom.
 10. A compound according to claim 1, wherein R¹ is —CH₂CH₂OH.
 11. A compound according to claim 1, wherein R¹ is selected from the group consisting of:


12. A compound according to claim 1, wherein the compound is selected from the group consisting of: Compound I: Deoxy-Actagardine B N-[2-ethanolamine]monocarboxamide; Compound II: Deoxy-Actagardine B N-[4-butanolamine]monocarboxamide; Compound III: Actagardine N[2-ethanolamine]monocarboxamide; Compound IV: Deoxy-actagardine B (3-amino-1,2-propanediol) monocarboxamide; Compound V: Deoxy-actagardine B (2-amino-1,3-propanol) monocarboxamide; Compound VI: Deoxy-actagardine B [tris(hydroxymethyl)methylamine]monocarboxamide; Compound VII: Deoxy-actagardine B (1-amino-2-propanol) monocarboxamide; Compound VIII: Deoxy-actagardine B (1-amino-3-propanol) monocarboxamide; Compound IX: (L)-Phenylalanyl-(O)-deoxyactagardine B (ethanolamine) monocarboxamide; Compound X: (L)-Tryptophanyl-(O)-deoxyactagardine B (ethanolamine) monocarboxamide; Compound XI: (L)-Alanyl-(O)-deoxyactagardine B (ethanolamine) monocarboxamide; Compound XII: (D)-Alanyl-(O)-deoxyactagardine B (ethanolamine) monocarboxamide; Compound XIII: (L)-Isoleucinyl-(O)-deoxyactagardine B (ethanolamine) monocarboxamide; Compound XIV: (L)-Leucinyl-(O)-deoxyactagardine B (ethanolamine) monocarboxamide; Compound XV: N-Phenylacetyl deoxyactagardine B (ethanolamine) monocarboxamide; Compound XVI: N-Acetyl deoxyactagardine B (ethanolamine) monocarboxamide; Compound XVII: N-Mandelyl deoxyactagardine B (ethanolamine) monocarboxamide; Compound XVIII: Deoxyactagardine B (N,N-bis(2-hydroxyethyl)ethylene diamine) monocarboxamide; Compound XX: Deoxy-Actagardine B N-[2-hydroxy-2-phenylethylamine]monocarboxamide; Compound XXI: Deoxy-actagardine B (L-serine methyl ester) monocarboxamide; Compound XXII: Deoxyactagardine B (N-(2-hydroxyethyl)ethylenediamine) monocarboxamide; Compound XXIII: Deoxy-actagardine B (2-hydroxypiperazine) monocarboxamide; Compound XXX: (L)-Alanyl-(O)-deoxyactagardine B (ethanolamine) monocarboxamide; Compound XXXI: (D)-Alanyl-(O)-deoxyactagardine B (ethanolamine) monocarboxamide; Compound XXXII: (L)-Isoleucinyl-(O)-deoxyactagardine B (ethanolamine) monocarboxamide; Compound XXXIII: (L)-Leucinyl-(O)-deoxyactagardine B (ethanolamine) monocarboxamide; Compound XXXIV: N-Phenylacetyl deoxyactagardine B (ethanolamine) monocarboxamide; Compound XXXV: N-Acetyl deoxyactagardine B (ethanolamine) monocarboxamide; and Compound XXXVI: N-Mandelyl deoxyactagardine B (ethanolamine) monocarboxamide.
 13. A variant of a compound as described in claim 1, wherein 1, 2, 3 or 4 amino acids are substituted by another amino acid.
 14. A variant according to claim 13, wherein the 1, 2, 3 or 4 amino acids are at positions selected from positions 2, 3, 4, 5, 8, 10, 11, 13, 15, 16 or 18 of the compound.
 15. A pharmaceutical composition comprising a compound according to claim 1 and a pharmaceutically acceptable carrier or diluent. 16-18. (canceled)
 19. A method for the treatment or prophylaxis of a microbial infection in a subject, the method comprising administering to said subject an effective amount of a compound according to claim
 1. 20. The method of claim 19, wherein the microbial infection is a bacterial infection.
 21. The method of claim 20, wherein the bacterial infection is an Enterococcus sp, Streptococcus spp, Staphylococcus spp. or Clostridium difficile infection.
 22. The method of claim 21, wherein the bacterial infection is a Clostridium difficile infection.
 23. A pharmaceutical composition comprising a variant according to claim 13 and a pharmaceutically acceptable carrier or diluent.
 24. A method for the treatment or prophylaxis of a microbial infection in a subject, the method comprising administering to said subject an effective amount of a variant according to claim
 13. 25. A method for the treatment or prophylaxis of a microbial infection in a subject, the method comprising administering to said subject an effective amount of a pharmaceutical composition according to claim
 15. 